diff --git a/consensus/quorum/quorom_test.go b/consensus/quorum/quorom_test.go
index a4e320029..80f55b2e1 100644
--- a/consensus/quorum/quorom_test.go
+++ b/consensus/quorum/quorom_test.go
@@ -1,11 +1,18 @@
 package quorum
 
 import (
+	"math/big"
+	"strings"
 	"testing"
 
+	bls_core "github.com/harmony-one/bls/ffi/go/bls"
 	harmony_bls "github.com/harmony-one/harmony/crypto/bls"
+	"github.com/harmony-one/harmony/internal/configs/sharding"
 	"github.com/harmony-one/harmony/shard"
 	"github.com/stretchr/testify/assert"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/harmony-one/harmony/crypto/bls"
 )
 
 func TestPhaseStrings(t *testing.T) {
@@ -59,3 +66,416 @@ func TestAddingQuoromParticipants(t *testing.T) {
 	decider.UpdateParticipants(blsKeys)
 	assert.Equal(t, keyCount, decider.ParticipantsCount())
 }
+
+func TestSubmitVote(test *testing.T) {
+	blockHash := [32]byte{}
+	copy(blockHash[:], []byte("random"))
+	blockNum := uint64(1000)
+	viewID := uint64(2)
+
+	decider := NewDecider(
+		SuperMajorityStake, shard.BeaconChainShardID,
+	)
+
+	message := "test string"
+	blsPriKey1 := bls.RandPrivateKey()
+	pubKeyWrapper1 := bls.PublicKeyWrapper{Object: blsPriKey1.GetPublicKey()}
+	pubKeyWrapper1.Bytes.FromLibBLSPublicKey(pubKeyWrapper1.Object)
+
+	blsPriKey2 := bls.RandPrivateKey()
+	pubKeyWrapper2 := bls.PublicKeyWrapper{Object: blsPriKey2.GetPublicKey()}
+	pubKeyWrapper2.Bytes.FromLibBLSPublicKey(pubKeyWrapper2.Object)
+
+	decider.UpdateParticipants([]bls.PublicKeyWrapper{pubKeyWrapper1, pubKeyWrapper2})
+
+	if _, err := decider.SubmitVote(
+		Prepare,
+		[]bls.SerializedPublicKey{pubKeyWrapper1.Bytes},
+		blsPriKey1.Sign(message),
+		common.BytesToHash(blockHash[:]),
+		blockNum,
+		viewID,
+	); err != nil {
+		test.Log(err)
+	}
+
+	if _, err := decider.SubmitVote(
+		Prepare,
+		[]bls.SerializedPublicKey{pubKeyWrapper2.Bytes},
+		blsPriKey2.Sign(message),
+		common.BytesToHash(blockHash[:]),
+		blockNum,
+		viewID,
+	); err != nil {
+		test.Log(err)
+	}
+	if decider.SignersCount(Prepare) != 2 {
+		test.Fatal("SubmitVote failed")
+	}
+
+	aggSig := &bls_core.Sign{}
+	aggSig.Add(blsPriKey1.Sign(message))
+	aggSig.Add(blsPriKey2.Sign(message))
+	if decider.AggregateVotes(Prepare).SerializeToHexStr() != aggSig.SerializeToHexStr() {
+		test.Fatal("AggregateVotes failed")
+	}
+}
+
+func TestSubmitVoteAggregateSig(test *testing.T) {
+	blockHash := [32]byte{}
+	copy(blockHash[:], []byte("random"))
+	blockNum := uint64(1000)
+	viewID := uint64(2)
+
+	decider := NewDecider(
+		SuperMajorityStake, shard.BeaconChainShardID,
+	)
+
+	blsPriKey1 := bls.RandPrivateKey()
+	pubKeyWrapper1 := bls.PublicKeyWrapper{Object: blsPriKey1.GetPublicKey()}
+	pubKeyWrapper1.Bytes.FromLibBLSPublicKey(pubKeyWrapper1.Object)
+
+	blsPriKey2 := bls.RandPrivateKey()
+	pubKeyWrapper2 := bls.PublicKeyWrapper{Object: blsPriKey2.GetPublicKey()}
+	pubKeyWrapper2.Bytes.FromLibBLSPublicKey(pubKeyWrapper2.Object)
+
+	blsPriKey3 := bls.RandPrivateKey()
+	pubKeyWrapper3 := bls.PublicKeyWrapper{Object: blsPriKey3.GetPublicKey()}
+	pubKeyWrapper3.Bytes.FromLibBLSPublicKey(pubKeyWrapper3.Object)
+
+	decider.UpdateParticipants([]bls.PublicKeyWrapper{pubKeyWrapper1, pubKeyWrapper2})
+
+	decider.SubmitVote(
+		Prepare,
+		[]bls.SerializedPublicKey{pubKeyWrapper1.Bytes},
+		blsPriKey1.SignHash(blockHash[:]),
+		common.BytesToHash(blockHash[:]),
+		blockNum,
+		viewID,
+	)
+
+	aggSig := &bls_core.Sign{}
+	for _, priKey := range []*bls_core.SecretKey{blsPriKey2, blsPriKey3} {
+		if s := priKey.SignHash(blockHash[:]); s != nil {
+			aggSig.Add(s)
+		}
+	}
+	if _, err := decider.SubmitVote(
+		Prepare,
+		[]bls.SerializedPublicKey{pubKeyWrapper2.Bytes, pubKeyWrapper3.Bytes},
+		aggSig,
+		common.BytesToHash(blockHash[:]),
+		blockNum,
+		viewID,
+	); err != nil {
+		test.Log(err)
+	}
+
+	if decider.SignersCount(Prepare) != 3 {
+		test.Fatal("SubmitVote failed")
+	}
+
+	aggSig.Add(blsPriKey1.SignHash(blockHash[:]))
+	if decider.AggregateVotes(Prepare).SerializeToHexStr() != aggSig.SerializeToHexStr() {
+		test.Fatal("AggregateVotes failed")
+	}
+
+	if _, err := decider.SubmitVote(
+		Prepare,
+		[]bls.SerializedPublicKey{pubKeyWrapper2.Bytes},
+		aggSig,
+		common.BytesToHash(blockHash[:]),
+		blockNum,
+		viewID,
+	); err == nil {
+		test.Fatal("Expect error for duplicate votes from the same key")
+	}
+}
+
+func TestAddNewVote(test *testing.T) {
+	shard.Schedule = shardingconfig.LocalnetSchedule
+	blockHash := [32]byte{}
+	copy(blockHash[:], []byte("random"))
+	blockNum := uint64(1000)
+	viewID := uint64(2)
+
+	decider := NewDecider(
+		SuperMajorityStake, shard.BeaconChainShardID,
+	)
+
+	slotList := shard.SlotList{}
+	sKeys := []bls_core.SecretKey{}
+	pubKeys := []bls.PublicKeyWrapper{}
+
+	quorumNodes := 10
+
+	for i := 0; i < quorumNodes; i++ {
+		newSlot, sKey := generateRandomSlot()
+		if i < 3 {
+			newSlot.EffectiveStake = nil
+		}
+		sKeys = append(sKeys, sKey)
+		slotList = append(slotList, newSlot)
+		wrapper := bls.PublicKeyWrapper{Object: sKey.GetPublicKey()}
+		wrapper.Bytes.FromLibBLSPublicKey(wrapper.Object)
+		pubKeys = append(pubKeys, wrapper)
+	}
+
+	decider.UpdateParticipants(pubKeys)
+	decider.SetVoters(&shard.Committee{
+		shard.BeaconChainShardID, slotList,
+	}, big.NewInt(3))
+
+	aggSig := &bls_core.Sign{}
+	for _, priKey := range []*bls_core.SecretKey{&sKeys[0], &sKeys[1], &sKeys[2]} {
+		if s := priKey.SignHash(blockHash[:]); s != nil {
+			aggSig.Add(s)
+		}
+	}
+
+	// aggregate sig from all of 3 harmony nodes
+	decider.AddNewVote(Prepare,
+		[]*bls.PublicKeyWrapper{&pubKeys[0], &pubKeys[1], &pubKeys[2]},
+		aggSig,
+		common.BytesToHash(blockHash[:]),
+		blockNum,
+		viewID)
+
+	if !decider.IsQuorumAchieved(Prepare) {
+		test.Error("quorum should have been achieved with harmony nodes")
+	}
+	if decider.SignersCount(Prepare) != 3 {
+		test.Errorf("signers are incorrect for harmony nodes signing with aggregate sig: have %d, expect %d", decider.SignersCount(Prepare), 3)
+	}
+
+	decider.ResetPrepareAndCommitVotes()
+
+	// aggregate sig from 3 external nodes, expect error
+	aggSig = &bls_core.Sign{}
+	for _, priKey := range []*bls_core.SecretKey{&sKeys[3], &sKeys[4], &sKeys[5]} {
+		if s := priKey.SignHash(blockHash[:]); s != nil {
+			aggSig.Add(s)
+		}
+	}
+	_, err := decider.AddNewVote(Prepare,
+		[]*bls.PublicKeyWrapper{&pubKeys[3], &pubKeys[4], &pubKeys[5]},
+		aggSig,
+		common.BytesToHash(blockHash[:]),
+		blockNum,
+		viewID)
+
+	if err == nil {
+		test.Error("Should have error due to aggregate sig from multiple accounts")
+	}
+	if decider.IsQuorumAchieved(Prepare) {
+		test.Fatal("quorum shouldn't have been achieved with external nodes")
+	}
+	if decider.SignersCount(Prepare) != 0 {
+		test.Errorf("signers are incorrect for harmony nodes signing with aggregate sig: have %d, expect %d", decider.SignersCount(Prepare), 0)
+	}
+
+	decider.ResetPrepareAndCommitVotes()
+
+	// one sig from external node
+	_, err = decider.AddNewVote(Prepare,
+		[]*bls.PublicKeyWrapper{&pubKeys[3]},
+		sKeys[3].SignHash(blockHash[:]),
+		common.BytesToHash(blockHash[:]),
+		blockNum,
+		viewID)
+	if err != nil {
+		test.Error(err)
+	}
+	if decider.IsQuorumAchieved(Prepare) {
+		test.Fatal("quorum shouldn't have been achieved with only one key signing")
+	}
+	if decider.SignersCount(Prepare) != 1 {
+		test.Errorf("signers are incorrect for harmony nodes signing with aggregate sig: have %d, expect %d", decider.SignersCount(Prepare), 1)
+	}
+}
+
+func TestAddNewVoteAggregateSig(test *testing.T) {
+	shard.Schedule = shardingconfig.LocalnetSchedule
+	blockHash := [32]byte{}
+	copy(blockHash[:], []byte("random"))
+	blockNum := uint64(1000)
+	viewID := uint64(2)
+
+	decider := NewDecider(
+		SuperMajorityStake, shard.BeaconChainShardID,
+	)
+
+	slotList := shard.SlotList{}
+	sKeys := []bls_core.SecretKey{}
+	pubKeys := []bls.PublicKeyWrapper{}
+
+	quorumNodes := 5
+
+	for i := 0; i < quorumNodes; i++ {
+		newSlot, sKey := generateRandomSlot()
+		if i < 3 {
+			newSlot.EffectiveStake = nil
+		}
+		sKeys = append(sKeys, sKey)
+		slotList = append(slotList, newSlot)
+		wrapper := bls.PublicKeyWrapper{Object: sKey.GetPublicKey()}
+		wrapper.Bytes.FromLibBLSPublicKey(wrapper.Object)
+		pubKeys = append(pubKeys, wrapper)
+	}
+
+	// make all external keys belong to same account
+	slotList[3].EcdsaAddress = slotList[4].EcdsaAddress
+
+	decider.UpdateParticipants(pubKeys)
+	decider.SetVoters(&shard.Committee{
+		shard.BeaconChainShardID, slotList,
+	}, big.NewInt(3))
+
+	aggSig := &bls_core.Sign{}
+	for _, priKey := range []*bls_core.SecretKey{&sKeys[0], &sKeys[1]} {
+		if s := priKey.SignHash(blockHash[:]); s != nil {
+			aggSig.Add(s)
+		}
+	}
+
+	// aggregate sig from all of 2 harmony nodes
+	decider.AddNewVote(Prepare,
+		[]*bls.PublicKeyWrapper{&pubKeys[0], &pubKeys[1]},
+		aggSig,
+		common.BytesToHash(blockHash[:]),
+		blockNum,
+		viewID)
+
+	if decider.IsQuorumAchieved(Prepare) {
+		test.Error("quorum should not have been achieved with 2 harmony nodes")
+	}
+	if decider.SignersCount(Prepare) != 2 {
+		test.Errorf("signers are incorrect for harmony nodes signing with aggregate sig: have %d, expect %d", decider.SignersCount(Prepare), 2)
+	}
+	// aggregate sig from all of 2 external nodes
+
+	aggSig = &bls_core.Sign{}
+	for _, priKey := range []*bls_core.SecretKey{&sKeys[3], &sKeys[4]} {
+		if s := priKey.SignHash(blockHash[:]); s != nil {
+			aggSig.Add(s)
+		}
+	}
+	decider.AddNewVote(Prepare,
+		[]*bls.PublicKeyWrapper{&pubKeys[3], &pubKeys[4]},
+		aggSig,
+		common.BytesToHash(blockHash[:]),
+		blockNum,
+		viewID)
+
+	if !decider.IsQuorumAchieved(Prepare) {
+		test.Error("quorum should have been achieved with 2 harmony nodes")
+	}
+	if decider.SignersCount(Prepare) != 4 {
+		test.Errorf("signers are incorrect for harmony nodes signing with aggregate sig: have %d, expect %d", decider.SignersCount(Prepare), 4)
+	}
+}
+
+func TestAddNewVoteInvalidAggregateSig(test *testing.T) {
+	shard.Schedule = shardingconfig.LocalnetSchedule
+	blockHash := [32]byte{}
+	copy(blockHash[:], []byte("random"))
+	blockNum := uint64(1000)
+	viewID := uint64(2)
+
+	decider := NewDecider(
+		SuperMajorityStake, shard.BeaconChainShardID,
+	)
+
+	slotList := shard.SlotList{}
+	sKeys := []bls_core.SecretKey{}
+	pubKeys := []bls.PublicKeyWrapper{}
+
+	quorumNodes := 8
+
+	for i := 0; i < quorumNodes; i++ {
+		newSlot, sKey := generateRandomSlot()
+		if i < 3 {
+			newSlot.EffectiveStake = nil
+		}
+		sKeys = append(sKeys, sKey)
+		slotList = append(slotList, newSlot)
+		wrapper := bls.PublicKeyWrapper{Object: sKey.GetPublicKey()}
+		wrapper.Bytes.FromLibBLSPublicKey(wrapper.Object)
+		pubKeys = append(pubKeys, wrapper)
+	}
+
+	// make all external keys belong to same account
+	slotList[3].EcdsaAddress = slotList[7].EcdsaAddress
+	slotList[4].EcdsaAddress = slotList[7].EcdsaAddress
+	slotList[5].EcdsaAddress = slotList[7].EcdsaAddress
+	slotList[6].EcdsaAddress = slotList[7].EcdsaAddress
+
+	decider.UpdateParticipants(pubKeys)
+	decider.SetVoters(&shard.Committee{
+		shard.BeaconChainShardID, slotList,
+	}, big.NewInt(3))
+
+	aggSig := &bls_core.Sign{}
+	for _, priKey := range []*bls_core.SecretKey{&sKeys[0], &sKeys[1]} {
+		if s := priKey.SignHash(blockHash[:]); s != nil {
+			aggSig.Add(s)
+		}
+	}
+
+	// aggregate sig from all of 2 harmony nodes
+	decider.AddNewVote(Prepare,
+		[]*bls.PublicKeyWrapper{&pubKeys[0], &pubKeys[1]},
+		aggSig,
+		common.BytesToHash(blockHash[:]),
+		blockNum,
+		viewID)
+
+	if decider.IsQuorumAchieved(Prepare) {
+		test.Error("quorum should not have been achieved with 2 harmony nodes")
+	}
+	if decider.SignersCount(Prepare) != 2 {
+		test.Errorf("signers are incorrect for harmony nodes signing with aggregate sig: have %d, expect %d", decider.SignersCount(Prepare), 2)
+	}
+	// aggregate sig from all of 2 external nodes
+	_, err := decider.AddNewVote(Prepare,
+		[]*bls.PublicKeyWrapper{&pubKeys[3], &pubKeys[4]},
+		aggSig,
+		common.BytesToHash(blockHash[:]),
+		blockNum,
+		viewID)
+
+	if err != nil {
+		test.Error(err, "expect no error")
+	}
+	if decider.SignersCount(Prepare) != 4 {
+		test.Errorf("signers are incorrect for harmony nodes signing with aggregate sig: have %d, expect %d", decider.SignersCount(Prepare), 4)
+	}
+
+	_, err = decider.AddNewVote(Prepare,
+		[]*bls.PublicKeyWrapper{&pubKeys[3], &pubKeys[7]},
+		aggSig,
+		common.BytesToHash(blockHash[:]),
+		blockNum,
+		viewID)
+
+	if !strings.Contains(err.Error(), "vote is already submitted") {
+		test.Error(err, "expect error due to already submitted votes")
+	}
+	if decider.SignersCount(Prepare) != 4 {
+		test.Errorf("signers are incorrect for harmony nodes signing with aggregate sig: have %d, expect %d", decider.SignersCount(Prepare), 4)
+	}
+
+	_, err = decider.AddNewVote(Prepare,
+		[]*bls.PublicKeyWrapper{&pubKeys[6], &pubKeys[5], &pubKeys[6]},
+		aggSig,
+		common.BytesToHash(blockHash[:]),
+		blockNum,
+		viewID)
+
+	if !strings.Contains(err.Error(), "duplicate key found in votes") {
+		test.Error(err, "expect error due to duplicate keys in aggregated votes")
+	}
+	if decider.SignersCount(Prepare) != 4 {
+		test.Errorf("signers are incorrect for harmony nodes signing with aggregate sig: have %d, expect %d", decider.SignersCount(Prepare), 4)
+	}
+}
diff --git a/consensus/quorum/quorum.go b/consensus/quorum/quorum.go
index a3f87e1e8..6b9b4e0ab 100644
--- a/consensus/quorum/quorum.go
+++ b/consensus/quorum/quorum.go
@@ -16,7 +16,7 @@ import (
 	"github.com/pkg/errors"
 )
 
-// MessageType is a phase that needs quorum to proceed
+// Phase is a phase that needs quorum to proceed
 type Phase byte
 
 const (
@@ -253,7 +253,13 @@ func (s *cIdentities) SubmitVote(
 	sig *bls_core.Sign, headerHash common.Hash,
 	height, viewID uint64,
 ) (*votepower.Ballot, error) {
+	seenKeys := map[bls.SerializedPublicKey]struct{}{}
 	for _, pubKey := range pubkeys {
+		if _, ok := seenKeys[pubKey]; ok {
+			return nil, errors.Errorf("duplicate key found in votes %x", pubKey)
+		}
+		seenKeys[pubKey] = struct{}{}
+
 		if ballet := s.ReadBallot(p, pubKey); ballet != nil {
 			return nil, errors.Errorf("vote is already submitted %x", pubKey)
 		}