diff --git a/core/src/main/java/org/apache/calcite/rex/RexSimplify.java b/core/src/main/java/org/apache/calcite/rex/RexSimplify.java
index 4d7702295bf..4477c24a520 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexSimplify.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexSimplify.java
@@ -408,6 +408,22 @@ RexNode isFalse(RexNode e) {
   private RexNode simplifyGenericNode(RexCall e) {
     final List<RexNode> operands = new ArrayList<>(e.operands);
     simplifyList(operands, UNKNOWN);
+
+    // Simplify CARDINALITY(MAP_KEYS(m)) -> CARDINALITY(m)
+    // and CARDINALITY(MAP_VALUES(m)) -> CARDINALITY(m)
+    if (e.getOperator().getName().equals("CARDINALITY")
+        && operands.size() == 1
+        && operands.get(0) instanceof RexCall) {
+      final RexCall innerCall = (RexCall) operands.get(0);
+      final SqlKind innerKind = innerCall.getKind();
+      if (innerKind == SqlKind.MAP_KEYS || innerKind == SqlKind.MAP_VALUES) {
+        // CARDINALITY(MAP_KEYS(m)) -> CARDINALITY(m)
+        // CARDINALITY(MAP_VALUES(m)) -> CARDINALITY(m)
+        final RexNode map = innerCall.getOperands().get(0);
+        return rexBuilder.makeCall(e.getParserPosition(), e.getOperator(), map);
+      }
+    }
+
     if (e.operands.equals(operands)) {
       return e;
     }
diff --git a/core/src/test/java/org/apache/calcite/rex/RexBuilderTest.java b/core/src/test/java/org/apache/calcite/rex/RexBuilderTest.java
index e23679eaf5f..a59b8949176 100644
--- a/core/src/test/java/org/apache/calcite/rex/RexBuilderTest.java
+++ b/core/src/test/java/org/apache/calcite/rex/RexBuilderTest.java
@@ -1524,4 +1524,64 @@ private static class UDT extends RelDataTypeImpl {
             literal, literal, flag),
         notNullValue());
   }
+
+  @Test void testCardinalityMapKeysSimplification() {
+    final RexImplicationCheckerFixtures.Fixture f =
+        new RexImplicationCheckerFixtures.Fixture();
+    final RexBuilder rexBuilder = f.rexBuilder;
+
+    // Create map literal: map['foo', 1, 'bar', 2]
+    final RexLiteral fooKey = rexBuilder.makeLiteral("foo");
+    final RexLiteral oneVal = rexBuilder.makeExactLiteral(new java.math.BigDecimal(1));
+    final RexLiteral barKey = rexBuilder.makeLiteral("bar");
+    final RexLiteral twoVal = rexBuilder.makeExactLiteral(new java.math.BigDecimal(2));
+    final RexNode mapLiteral =
+        rexBuilder.makeCall(SqlStdOperatorTable.MAP_VALUE_CONSTRUCTOR,
+        fooKey, oneVal, barKey, twoVal);
+
+    // Create CARDINALITY(MAP_KEYS(map))
+    final RexNode mapKeys =
+        rexBuilder.makeCall(SqlLibraryOperators.MAP_KEYS, mapLiteral);
+    final RexNode cardinalityMapKeys =
+        rexBuilder.makeCall(SqlStdOperatorTable.CARDINALITY, mapKeys);
+
+    // Simplify
+    final RexNode simplified = f.simplify.simplify(cardinalityMapKeys);
+
+    // Expected: CARDINALITY(map)
+    final RexNode expectedCardinalityMap =
+        rexBuilder.makeCall(SqlStdOperatorTable.CARDINALITY, mapLiteral);
+
+    assertThat(simplified, hasToString(expectedCardinalityMap.toString()));
+  }
+
+  @Test void testCardinalityMapValuesSimplification() {
+    final RexImplicationCheckerFixtures.Fixture f =
+        new RexImplicationCheckerFixtures.Fixture();
+    final RexBuilder rexBuilder = f.rexBuilder;
+
+    // Create map literal: map['foo', 1, 'bar', 2]
+    final RexLiteral fooKey = rexBuilder.makeLiteral("foo");
+    final RexLiteral oneVal = rexBuilder.makeExactLiteral(new java.math.BigDecimal(1));
+    final RexLiteral barKey = rexBuilder.makeLiteral("bar");
+    final RexLiteral twoVal = rexBuilder.makeExactLiteral(new java.math.BigDecimal(2));
+    final RexNode mapLiteral =
+        rexBuilder.makeCall(SqlStdOperatorTable.MAP_VALUE_CONSTRUCTOR,
+        fooKey, oneVal, barKey, twoVal);
+
+    // Create CARDINALITY(MAP_VALUES(map))
+    final RexNode mapValues =
+        rexBuilder.makeCall(SqlLibraryOperators.MAP_VALUES, mapLiteral);
+    final RexNode cardinalityMapValues =
+        rexBuilder.makeCall(SqlStdOperatorTable.CARDINALITY, mapValues);
+
+    // Simplify
+    final RexNode simplified = f.simplify.simplify(cardinalityMapValues);
+
+    // Expected: CARDINALITY(map)
+    final RexNode expectedCardinalityMap =
+        rexBuilder.makeCall(SqlStdOperatorTable.CARDINALITY, mapLiteral);
+
+    assertThat(simplified, hasToString(expectedCardinalityMap.toString()));
+  }
 }