diff --git a/spanner/client_test.go b/spanner/client_test.go
index ccd25d8f49c9..f29b6dc72ac0 100644
--- a/spanner/client_test.go
+++ b/spanner/client_test.go
@@ -1036,6 +1036,88 @@ func TestClient_ReadWriteTransactionWithOptions(t *testing.T) {
 	}
 }
 
+func TestClient_ReadWriteTransactionWithOptimisticLockMode_ExecuteSqlRequest(t *testing.T) {
+	server, client, teardown := setupMockedTestServer(t)
+	defer teardown()
+	ctx := context.Background()
+	server.TestSpanner.PutExecutionTime(MethodExecuteStreamingSql,
+		SimulatedExecutionTime{
+			Errors: []error{status.Error(codes.Unavailable, "Temporary unavailable"), status.Error(codes.Aborted, "Transaction aborted")},
+		})
+	_, err := client.ReadWriteTransactionWithOptions(ctx, func(ctx context.Context, tx *ReadWriteTransaction) error {
+		iter := tx.Query(ctx, NewStatement(SelectSingerIDAlbumIDAlbumTitleFromAlbums))
+		defer iter.Stop()
+		_, err := iter.Next()
+		return err
+	}, TransactionOptions{ReadLockMode: sppb.TransactionOptions_ReadWrite_OPTIMISTIC})
+	if err != nil {
+		t.Fatalf("Failed to execute the transaction: %s", err)
+	}
+	requests := drainRequestsFromServer(server.TestSpanner)
+	if err := compareRequests([]interface{}{
+		&sppb.BatchCreateSessionsRequest{},
+		&sppb.ExecuteSqlRequest{},
+		&sppb.ExecuteSqlRequest{},
+		&sppb.BeginTransactionRequest{},
+		&sppb.ExecuteSqlRequest{},
+		&sppb.CommitRequest{}}, requests); err != nil {
+		t.Fatal(err)
+	}
+	if requests[1].(*sppb.ExecuteSqlRequest).GetTransaction().GetBegin().GetReadWrite().GetReadLockMode() != sppb.TransactionOptions_ReadWrite_OPTIMISTIC {
+		t.Fatal("Transaction is not set to optimistic")
+	}
+	if requests[2].(*sppb.ExecuteSqlRequest).GetTransaction().GetBegin().GetReadWrite().GetReadLockMode() != sppb.TransactionOptions_ReadWrite_OPTIMISTIC {
+		t.Fatal("Transaction is not set to optimistic")
+	}
+	if requests[3].(*sppb.BeginTransactionRequest).GetOptions().GetReadWrite().GetReadLockMode() != sppb.TransactionOptions_ReadWrite_OPTIMISTIC {
+		t.Fatal("Begin Transaction is not set to optimistic")
+	}
+	if _, ok := requests[4].(*sppb.ExecuteSqlRequest).Transaction.GetSelector().(*sppb.TransactionSelector_Id); !ok {
+		t.Fatal("expected streaming query to use transactionID from explicit begin transaction")
+	}
+}
+
+func TestClient_ReadWriteTransactionWithOptimisticLockMode_ReadRequest(t *testing.T) {
+	server, client, teardown := setupMockedTestServer(t)
+	defer teardown()
+	ctx := context.Background()
+	server.TestSpanner.PutExecutionTime(MethodStreamingRead,
+		SimulatedExecutionTime{
+			Errors: []error{status.Error(codes.Unavailable, "Temporary unavailable"), status.Error(codes.Aborted, "Transaction aborted")},
+		})
+	_, err := client.ReadWriteTransactionWithOptions(ctx, func(ctx context.Context, tx *ReadWriteTransaction) error {
+		iter := tx.Read(ctx, "Albums", KeySets(Key{"foo"}), []string{"SingerId", "AlbumId", "AlbumTitle"})
+		defer iter.Stop()
+		_, err := iter.Next()
+		return err
+	}, TransactionOptions{ReadLockMode: sppb.TransactionOptions_ReadWrite_OPTIMISTIC})
+	if err != nil {
+		t.Fatalf("Failed to execute the transaction: %s", err)
+	}
+	requests := drainRequestsFromServer(server.TestSpanner)
+	if err := compareRequests([]interface{}{
+		&sppb.BatchCreateSessionsRequest{},
+		&sppb.ReadRequest{},
+		&sppb.ReadRequest{},
+		&sppb.BeginTransactionRequest{},
+		&sppb.ReadRequest{},
+		&sppb.CommitRequest{}}, requests); err != nil {
+		t.Fatal(err)
+	}
+	if requests[1].(*sppb.ReadRequest).GetTransaction().GetBegin().GetReadWrite().GetReadLockMode() != sppb.TransactionOptions_ReadWrite_OPTIMISTIC {
+		t.Fatal("Transaction is not set to optimistic")
+	}
+	if requests[2].(*sppb.ReadRequest).GetTransaction().GetBegin().GetReadWrite().GetReadLockMode() != sppb.TransactionOptions_ReadWrite_OPTIMISTIC {
+		t.Fatal("Transaction is not set to optimistic")
+	}
+	if requests[3].(*sppb.BeginTransactionRequest).GetOptions().GetReadWrite().GetReadLockMode() != sppb.TransactionOptions_ReadWrite_OPTIMISTIC {
+		t.Fatal("Begin Transaction is not set to optimistic")
+	}
+	if _, ok := requests[4].(*sppb.ReadRequest).Transaction.GetSelector().(*sppb.TransactionSelector_Id); !ok {
+		t.Fatal("expected streaming read to use transactionID from explicit begin transaction")
+	}
+}
+
 func TestClient_ReadWriteStmtBasedTransaction_TransactionOptions(t *testing.T) {
 	for _, tt := range transactionOptionsTestCases() {
 		t.Run(tt.name, func(t *testing.T) {
@@ -2999,6 +3081,12 @@ func transactionOptionsTestCases() []TransactionOptionsTestCase {
 			write:  &TransactionOptions{CommitOptions: CommitOptions{ReturnCommitStats: true}, TransactionTag: "writeTransactionTag", CommitPriority: sppb.RequestOptions_PRIORITY_MEDIUM},
 			want:   &TransactionOptions{CommitOptions: CommitOptions{ReturnCommitStats: true}, TransactionTag: "writeTransactionTag", CommitPriority: sppb.RequestOptions_PRIORITY_MEDIUM},
 		},
+		{
+			name:   "Read lock mode is optimistic",
+			client: &TransactionOptions{ReadLockMode: sppb.TransactionOptions_ReadWrite_OPTIMISTIC},
+			write:  &TransactionOptions{},
+			want:   &TransactionOptions{},
+		},
 	}
 }
 
diff --git a/spanner/transaction.go b/spanner/transaction.go
index d28dc25ffc12..4179c8689bd0 100644
--- a/spanner/transaction.go
+++ b/spanner/transaction.go
@@ -103,6 +103,10 @@ type TransactionOptions struct {
 	// CommitPriority is the priority to use for the Commit RPC for the
 	// transaction.
 	CommitPriority sppb.RequestOptions_Priority
+
+	// the transaction lock mode is used to specify a concurrency mode for the
+	// read/query operations. It works for a read/write transaction only.
+	ReadLockMode sppb.TransactionOptions_ReadWrite_ReadLockMode
 }
 
 // merge combines two TransactionOptions that the input parameter will have higher
@@ -119,6 +123,9 @@ func (to TransactionOptions) merge(opts TransactionOptions) TransactionOptions {
 	if opts.CommitPriority != sppb.RequestOptions_PRIORITY_UNSPECIFIED {
 		merged.CommitPriority = opts.CommitPriority
 	}
+	if opts.ReadLockMode != sppb.TransactionOptions_ReadWrite_READ_LOCK_MODE_UNSPECIFIED {
+		merged.ReadLockMode = opts.ReadLockMode
+	}
 	return merged
 }
 
@@ -1244,7 +1251,9 @@ func (t *ReadWriteTransaction) getTransactionSelector() *sppb.TransactionSelecto
 		Selector: &sppb.TransactionSelector_Begin{
 			Begin: &sppb.TransactionOptions{
 				Mode: &sppb.TransactionOptions_ReadWrite_{
-					ReadWrite: &sppb.TransactionOptions_ReadWrite{},
+					ReadWrite: &sppb.TransactionOptions_ReadWrite{
+						ReadLockMode: t.txOpts.ReadLockMode,
+					},
 				},
 			},
 		},
@@ -1278,12 +1287,14 @@ func (t *ReadWriteTransaction) release(err error) {
 	}
 }
 
-func beginTransaction(ctx context.Context, sid string, client *vkit.Client) (transactionID, error) {
+func beginTransaction(ctx context.Context, sid string, client *vkit.Client, opts TransactionOptions) (transactionID, error) {
 	res, err := client.BeginTransaction(ctx, &sppb.BeginTransactionRequest{
 		Session: sid,
 		Options: &sppb.TransactionOptions{
 			Mode: &sppb.TransactionOptions_ReadWrite_{
-				ReadWrite: &sppb.TransactionOptions_ReadWrite{},
+				ReadWrite: &sppb.TransactionOptions_ReadWrite{
+					ReadLockMode: opts.ReadLockMode,
+				},
 			},
 		},
 	})
@@ -1344,7 +1355,7 @@ func (t *ReadWriteTransaction) begin(ctx context.Context) error {
 				return err
 			}
 		}
-		tx, err = beginTransaction(contextWithOutgoingMetadata(ctx, sh.getMetadata()), sh.getID(), sh.getClient())
+		tx, err = beginTransaction(contextWithOutgoingMetadata(ctx, sh.getMetadata()), sh.getID(), sh.getClient(), t.txOpts)
 		if isSessionNotFoundError(err) {
 			sh.destroy()
 			continue