diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala
index f21aa1e9e313..a95ebe301b9d 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala
@@ -282,6 +282,8 @@ case class Cast(child: Expression, dataType: DataType, timeZoneId: Option[String
         builder.append("]")
         builder.build()
       })
+    case udt: UserDefinedType[_] =>
+      buildCast[Any](_, o => UTF8String.fromString(udt.deserialize(o).toString))
     case _ => buildCast[Any](_, o => UTF8String.fromString(o.toString))
   }
 
@@ -836,6 +838,11 @@ case class Cast(child: Expression, dataType: DataType, timeZoneId: Option[String
              |$evPrim = $buffer.build();
            """.stripMargin
         }
+      case udt: UserDefinedType[_] =>
+        val udtRef = ctx.addReferenceObj("udt", udt)
+        (c, evPrim, evNull) => {
+          s"$evPrim = UTF8String.fromString($udtRef.deserialize($c).toString());"
+        }
       case _ =>
         (c, evPrim, evNull) => s"$evPrim = UTF8String.fromString(String.valueOf($c));"
     }
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/UserDefinedTypeSuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/UserDefinedTypeSuite.scala
index a08433ba794d..cc8b600efa46 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/UserDefinedTypeSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/UserDefinedTypeSuite.scala
@@ -21,7 +21,7 @@ import scala.beans.{BeanInfo, BeanProperty}
 
 import org.apache.spark.rdd.RDD
 import org.apache.spark.sql.catalyst.{CatalystTypeConverters, InternalRow}
-import org.apache.spark.sql.catalyst.expressions.GenericInternalRow
+import org.apache.spark.sql.catalyst.expressions.{Cast, ExpressionEvalHelper, GenericInternalRow, Literal}
 import org.apache.spark.sql.catalyst.util.{ArrayData, GenericArrayData}
 import org.apache.spark.sql.execution.datasources.parquet.ParquetTest
 import org.apache.spark.sql.functions._
@@ -44,6 +44,8 @@ object UDT {
       case v: MyDenseVector => java.util.Arrays.equals(this.data, v.data)
       case _ => false
     }
+
+    override def toString: String = data.mkString("(", ", ", ")")
   }
 
   private[sql] class MyDenseVectorUDT extends UserDefinedType[MyDenseVector] {
@@ -143,7 +145,8 @@ private[spark] class ExampleSubTypeUDT extends UserDefinedType[IExampleSubType]
   override def userClass: Class[IExampleSubType] = classOf[IExampleSubType]
 }
 
-class UserDefinedTypeSuite extends QueryTest with SharedSQLContext with ParquetTest {
+class UserDefinedTypeSuite extends QueryTest with SharedSQLContext with ParquetTest
+    with ExpressionEvalHelper {
   import testImplicits._
 
   private lazy val pointsRDD = Seq(
@@ -304,4 +307,12 @@ class UserDefinedTypeSuite extends QueryTest with SharedSQLContext with ParquetT
       pointsRDD.except(pointsRDD2),
       Seq(Row(0.0, new UDT.MyDenseVector(Array(0.2, 2.0)))))
   }
+
+  test("SPARK-23054 Cast UserDefinedType to string") {
+    val udt = new UDT.MyDenseVectorUDT()
+    val vector = new UDT.MyDenseVector(Array(1.0, 3.0, 5.0, 7.0, 9.0))
+    val data = udt.serialize(vector)
+    val ret = Cast(Literal(data, udt), StringType, None)
+    checkEvaluation(ret, "(1.0, 3.0, 5.0, 7.0, 9.0)")
+  }
 }