diff --git a/docs/source/user-guide/latest/expressions.md b/docs/source/user-guide/latest/expressions.md
index 57b7a3455a..bb748f77e5 100644
--- a/docs/source/user-guide/latest/expressions.md
+++ b/docs/source/user-guide/latest/expressions.md
@@ -117,6 +117,7 @@ Expressions that are not Spark-compatible will fall back to Spark by default and
 | DayOfYear      | `dayofyear`                  | Yes               |                                                                                                                                  |
 | WeekOfYear     | `weekofyear`                 | Yes               |                                                                                                                                  |
 | Quarter        | `quarter`                    | Yes               |                                                                                                                                  |
+| PreciseTimestampConversion | `window_time`  | Yes               | Only supports conversions between TimestampType and LongType                                                                      |
 
 ## Math Expressions
 
diff --git a/spark/src/main/scala/org/apache/comet/serde/QueryPlanSerde.scala b/spark/src/main/scala/org/apache/comet/serde/QueryPlanSerde.scala
index 8c39ba779d..18bb4666a1 100644
--- a/spark/src/main/scala/org/apache/comet/serde/QueryPlanSerde.scala
+++ b/spark/src/main/scala/org/apache/comet/serde/QueryPlanSerde.scala
@@ -215,7 +215,8 @@ object QueryPlanSerde extends Logging with CometExprShim {
     classOf[WeekDay] -> CometWeekDay,
     classOf[DayOfYear] -> CometDayOfYear,
     classOf[WeekOfYear] -> CometWeekOfYear,
-    classOf[Quarter] -> CometQuarter)
+    classOf[Quarter] -> CometQuarter,
+    classOf[PreciseTimestampConversion] -> CometPreciseTimestampConversion)
 
   private val conversionExpressions: Map[Class[_ <: Expression], CometExpressionSerde[_]] = Map(
     classOf[Cast] -> CometCast)
diff --git a/spark/src/main/scala/org/apache/comet/serde/datetime.scala b/spark/src/main/scala/org/apache/comet/serde/datetime.scala
index 0720f785dd..ef20892575 100644
--- a/spark/src/main/scala/org/apache/comet/serde/datetime.scala
+++ b/spark/src/main/scala/org/apache/comet/serde/datetime.scala
@@ -21,8 +21,8 @@ package org.apache.comet.serde
 
 import java.util.Locale
 
-import org.apache.spark.sql.catalyst.expressions.{Attribute, DateAdd, DateDiff, DateFormatClass, DateSub, DayOfMonth, DayOfWeek, DayOfYear, GetDateField, Hour, LastDay, Literal, MakeDate, Minute, Month, NextDay, Quarter, Second, TruncDate, TruncTimestamp, UnixDate, UnixTimestamp, WeekDay, WeekOfYear, Year}
-import org.apache.spark.sql.types.{DateType, IntegerType, StringType, TimestampType}
+import org.apache.spark.sql.catalyst.expressions.{Attribute, DateAdd, DateDiff, DateFormatClass, DateSub, DayOfMonth, DayOfWeek, DayOfYear, GetDateField, Hour, LastDay, Literal, MakeDate, Minute, Month, NextDay, PreciseTimestampConversion, Quarter, Second, TruncDate, TruncTimestamp, UnixDate, UnixTimestamp, WeekDay, WeekOfYear, Year}
+import org.apache.spark.sql.types.{DateType, IntegerType, LongType, StringType, TimestampType}
 import org.apache.spark.unsafe.types.UTF8String
 
 import org.apache.comet.CometSparkSessionExtensions.withInfo
@@ -586,3 +586,22 @@ object CometDateFormat extends CometExpressionSerde[DateFormatClass] {
     }
   }
 }
+
+object CometPreciseTimestampConversion extends CometExpressionSerde[PreciseTimestampConversion] {
+  override def getSupportLevel(expr: PreciseTimestampConversion): SupportLevel = {
+    (expr.fromType, expr.toType) match {
+      case (TimestampType, LongType) | (LongType, TimestampType) =>
+        Compatible()
+      case _ =>
+        Unsupported(Some(s"PreciseTimestampConversion from ${expr.fromType} to ${expr.toType}"))
+    }
+  }
+
+  override def convert(
+      expr: PreciseTimestampConversion,
+      inputs: Seq[Attribute],
+      binding: Boolean): Option[ExprOuterClass.Expr] = {
+    // Both types are i64 micros in Arrow, so no conversion needed — return child directly.
+    exprToProtoInternal(expr.child, inputs, binding)
+  }
+}
diff --git a/spark/src/test/resources/sql-tests/expressions/datetime/window_time.sql b/spark/src/test/resources/sql-tests/expressions/datetime/window_time.sql
new file mode 100644
index 0000000000..79c7be40c9
--- /dev/null
+++ b/spark/src/test/resources/sql-tests/expressions/datetime/window_time.sql
@@ -0,0 +1,33 @@
+-- Licensed to the Apache Software Foundation (ASF) under one
+-- or more contributor license agreements.  See the NOTICE file
+-- distributed with this work for additional information
+-- regarding copyright ownership.  The ASF licenses this file
+-- to you under the Apache License, Version 2.0 (the
+-- "License"); you may not use this file except in compliance
+-- with the License.  You may obtain a copy of the License at
+--
+--   http://www.apache.org/licenses/LICENSE-2.0
+--
+-- Unless required by applicable law or agreed to in writing,
+-- software distributed under the License is distributed on an
+-- "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+-- KIND, either express or implied.  See the License for the
+-- specific language governing permissions and limitations
+-- under the License.
+
+
+statement
+CREATE TABLE test_window_time(time timestamp, value int) USING parquet
+
+statement
+INSERT INTO test_window_time VALUES (timestamp('2023-01-01 12:00:00'), 1), (timestamp('2023-01-01 12:05:00'), 2), (timestamp('2023-01-01 12:15:00'), 3), (NULL, 4)
+
+-- spark_answer_only: window() uses unsupported CreateNamedStruct and KnownNullable
+
+-- basic window_time with tumbling window
+query spark_answer_only
+SELECT max(window_time(window)), sum(value) FROM (SELECT window(time, '10 minutes') AS window, value FROM test_window_time) GROUP BY window
+
+-- window_time with sliding window
+query spark_answer_only
+SELECT max(window_time(window)), count(value) FROM (SELECT window(time, '10 minutes', '5 minutes') AS window, value FROM test_window_time) GROUP BY window