diff --git a/java-spanner-jdbc/src/main/java/com/google/cloud/spanner/jdbc/AbstractJdbcConnection.java b/java-spanner-jdbc/src/main/java/com/google/cloud/spanner/jdbc/AbstractJdbcConnection.java
index 26fcf3cd6503..9d199be5db62 100644
--- a/java-spanner-jdbc/src/main/java/com/google/cloud/spanner/jdbc/AbstractJdbcConnection.java
+++ b/java-spanner-jdbc/src/main/java/com/google/cloud/spanner/jdbc/AbstractJdbcConnection.java
@@ -155,12 +155,19 @@ public void setTransactionIsolation(int level) throws SQLException {
   @Override
   public int getTransactionIsolation() throws SQLException {
     checkClosed();
-    IsolationLevel isolationLevel = spanner.getDefaultIsolationLevel();
+    IsolationLevel isolationLevel =
+        spanner.isInTransaction()
+            ? spanner.getTransactionIsolationLevel()
+            : spanner.getDefaultIsolationLevel();
     if (isolationLevel == IsolationLevel.ISOLATION_LEVEL_UNSPECIFIED) {
       return JdbcDatabaseMetaData.getDatabaseDefaultTransactionIsolation(getDatabaseClient());
     }
-    //noinspection MagicConstant
-    return IsolationLevelConverter.convertToJdbc(isolationLevel);
+    try {
+      //noinspection MagicConstant
+      return IsolationLevelConverter.convertToJdbc(isolationLevel);
+    } catch (IllegalArgumentException e) {
+      throw JdbcSqlExceptionFactory.of(e.getMessage(), Code.INVALID_ARGUMENT, e);
+    }
   }
 
   @Override
diff --git a/java-spanner-jdbc/src/test/java/com/google/cloud/spanner/jdbc/TransactionMockServerTest.java b/java-spanner-jdbc/src/test/java/com/google/cloud/spanner/jdbc/TransactionMockServerTest.java
index 6aef833c1124..3793b174ba3d 100644
--- a/java-spanner-jdbc/src/test/java/com/google/cloud/spanner/jdbc/TransactionMockServerTest.java
+++ b/java-spanner-jdbc/src/test/java/com/google/cloud/spanner/jdbc/TransactionMockServerTest.java
@@ -130,7 +130,11 @@ public void testUsesManualIsolationLevel() throws SQLException {
             .createStatement()
             .execute(
                 "begin transaction isolation level " + isolationLevel.toString().replace("_", " "));
+        assertEquals(
+            IsolationLevelConverter.convertToJdbc(isolationLevel),
+            connection.getTransactionIsolation());
         runTestTransaction(connection, isolationLevel);
+        assertEquals(Connection.TRANSACTION_SERIALIZABLE, connection.getTransactionIsolation());
       }
     }
   }
diff --git a/java-spanner/google-cloud-spanner/clirr-ignored-differences.xml b/java-spanner/google-cloud-spanner/clirr-ignored-differences.xml
index 6ae30aeebe3f..454f91f82b08 100644
--- a/java-spanner/google-cloud-spanner/clirr-ignored-differences.xml
+++ b/java-spanner/google-cloud-spanner/clirr-ignored-differences.xml
@@ -1062,6 +1062,11 @@
     <className>com/google/cloud/spanner/connection/Connection</className>
     <method>java.lang.Object getConnectionPropertyValue(com.google.cloud.spanner.connection.ConnectionProperty)</method>
   </difference>
+  <difference>
+    <differenceType>7012</differenceType>
+    <className>com/google/cloud/spanner/connection/Connection</className>
+    <method>com.google.spanner.v1.TransactionOptions$IsolationLevel getTransactionIsolationLevel()</method>
+  </difference>
   <!-- (Remove since these methods has no usage. CompositeTracer interface is annotated as internal API) -->
   <difference>
     <differenceType>7002</differenceType>
diff --git a/java-spanner/google-cloud-spanner/src/main/java/com/google/cloud/spanner/connection/Connection.java b/java-spanner/google-cloud-spanner/src/main/java/com/google/cloud/spanner/connection/Connection.java
index 60d739a3c850..886b169948bc 100644
--- a/java-spanner/google-cloud-spanner/src/main/java/com/google/cloud/spanner/connection/Connection.java
+++ b/java-spanner/google-cloud-spanner/src/main/java/com/google/cloud/spanner/connection/Connection.java
@@ -1584,6 +1584,15 @@ default DatabaseClient getDatabaseClient() {
     throw new UnsupportedOperationException("Not implemented");
   }
 
+  /**
+   * @return the isolation level of the current transaction. This method may only be called when the
+   *     connection is in a transaction.
+   */
+  @InternalApi
+  default IsolationLevel getTransactionIsolationLevel() {
+    throw new UnsupportedOperationException("Not implemented");
+  }
+
   /** The {@link Spanner} instance that is used by this {@link Connection}. */
   @InternalApi
   default Spanner getSpanner() {
diff --git a/java-spanner/google-cloud-spanner/src/main/java/com/google/cloud/spanner/connection/ConnectionImpl.java b/java-spanner/google-cloud-spanner/src/main/java/com/google/cloud/spanner/connection/ConnectionImpl.java
index a1ed225c71cc..7cf407fc9fad 100644
--- a/java-spanner/google-cloud-spanner/src/main/java/com/google/cloud/spanner/connection/ConnectionImpl.java
+++ b/java-spanner/google-cloud-spanner/src/main/java/com/google/cloud/spanner/connection/ConnectionImpl.java
@@ -930,7 +930,8 @@ public void setTransactionMode(TransactionMode transactionMode) {
     this.unitOfWorkType = UnitOfWorkType.of(transactionMode);
   }
 
-  IsolationLevel getTransactionIsolationLevel() {
+  @Override
+  public IsolationLevel getTransactionIsolationLevel() {
     ConnectionPreconditions.checkState(!isClosed(), CLOSED_ERROR_MSG);
     ConnectionPreconditions.checkState(!isDdlBatchActive(), "This connection is in a DDL batch");
     ConnectionPreconditions.checkState(isInTransaction(), "This connection has no transaction");