diff --git a/FSharp.Json.Tests/Union.fs b/FSharp.Json.Tests/Union.fs
index 0de36fb..9d33673 100644
--- a/FSharp.Json.Tests/Union.fs
+++ b/FSharp.Json.Tests/Union.fs
@@ -95,7 +95,32 @@ module Union =
         let actual = Json.serializeU value
         let expected = """{"casekey":"StringCase","casevalue":"The string"}"""
         Assert.AreEqual(expected, actual)
-
+        
+    [<JsonUnion(Mode = UnionMode.AsValue)>]
+    type AsValueUnion =
+    | StringCase of string
+    | IntCase of int
+    
+    type RecordWithAsValueUnion = {
+        StringValue : AsValueUnion
+        IntValue : AsValueUnion
+    }
+    
+    [<Test>]
+    let ``Union AsValue serialization`` () =
+        let record = { StringValue = StringCase "String"; IntValue = IntCase 1 }
+        let actual = Json.serializeU record
+        let expected = """{"StringValue":"String","IntValue":1}"""
+        Assert.AreEqual(expected, actual)
+    
+    [<Test>]
+    let ``Union AsValue deserialization`` () =
+        let json = """{"StringValue":"String"}"""
+        let ex = Assert.Throws<JsonDeserializationError>(fun () -> Json.deserialize<RecordWithAsValueUnion> json |> ignore)
+        Assert.IsNotNull(ex)
+        let expectedPath = "StringValue"
+        Assert.AreEqual(expectedPath, ex.Path.toString())
+    
     [<Test>]
     let ``Union key-value deserialization`` () =
         let expected = TheAnnotatedUnion.StringCase "The string"
diff --git a/FSharp.Json/Core.fs b/FSharp.Json/Core.fs
index 747fc17..e4bad33 100644
--- a/FSharp.Json/Core.fs
+++ b/FSharp.Json/Core.fs
@@ -1,5 +1,8 @@
 namespace FSharp.Json
 
+open FSharp.Json
+open FSharp.Json.Internalized.FSharp.Data
+
 module internal Core =
     open System
     open System.Globalization
@@ -248,9 +251,10 @@ module internal Core =
                     match jsonUnion.Mode with
                     | UnionMode.CaseKeyAsFieldName -> JsonValue.Record [| (theCase, jValue) |]
                     | UnionMode.CaseKeyAsFieldValue ->
-                        let jKey = (jsonUnion.CaseKeyField, JsonValue.String theCase)
+                        let jkey = (jsonUnion.CaseKeyField, JsonValue.String theCase)
                         let jValue = (jsonUnion.CaseValueField, jValue)
-                        JsonValue.Record [| jKey; jValue |]
+                        JsonValue.Record [| jkey; jValue |]
+                    | UnionMode.AsValue -> jValue
                     | UnionMode.CaseKeyDiscriminatorField ->
                         match jValue with
                         | JsonValue.Record jRecord ->
@@ -519,6 +523,7 @@ module internal Core =
                 FSharpValue.MakeUnion (caseInfo, values)
             | _ ->
                 match jvalue with
+                | _ when jsonUnion.Mode = UnionMode.AsValue -> failDeserialization path "Failed to parse union from JSON: Union with AsValue Mode can't be parsed"
                 | JsonValue.String caseName ->
                     FSharpValue.MakeUnion (caseName |> getUnionCaseInfo path t, null)
                 | JsonValue.Record fields ->
@@ -550,4 +555,4 @@ module internal Core =
         | t when isTuple t -> deserializeTuple path t jValue
         | t when isUnion t -> deserializeUnion path t jValue
         | _ -> failDeserialization path $"Failed to serialize, must be one of following types: record, map, array, list, tuple, union. Type is: %s{t.Name}."
-    
\ No newline at end of file
+    
diff --git a/FSharp.Json/InterfaceTypes.fs b/FSharp.Json/InterfaceTypes.fs
index c8ce7a5..8501d14 100644
--- a/FSharp.Json/InterfaceTypes.fs
+++ b/FSharp.Json/InterfaceTypes.fs
@@ -50,6 +50,8 @@ type UnionMode =
     | CaseKeyAsFieldValue = 1
     /// Serialize union case key as discriminator field value.
     | CaseKeyDiscriminatorField = 2
+    /// Serialize union case as value.
+    | AsValue = 3
 
 /// Attribute customizing serialization of union types
 type JsonUnion () =