diff --git a/src/ModelContextProtocol.Core/Server/AIFunctionMcpServerTool.cs b/src/ModelContextProtocol.Core/Server/AIFunctionMcpServerTool.cs
index 82b6ceb9d..e8477854e 100644
--- a/src/ModelContextProtocol.Core/Server/AIFunctionMcpServerTool.cs
+++ b/src/ModelContextProtocol.Core/Server/AIFunctionMcpServerTool.cs
@@ -6,6 +6,7 @@
 using System.Reflection;
 using System.Text.Json;
 using System.Text.Json.Nodes;
+using System.Text.Json.Serialization;
 using System.Text.RegularExpressions;
 
 namespace ModelContextProtocol.Server;
@@ -14,6 +15,7 @@ namespace ModelContextProtocol.Server;
 internal sealed partial class AIFunctionMcpServerTool : McpServerTool
 {
     private readonly IReadOnlyList<object> _metadata;
+    private readonly JsonSerializerOptions _structuredContentSerializerOptions;
 
     /// <summary>
     /// Creates an <see cref="McpServerTool"/> instance for a method, specified via a <see cref="Delegate"/> instance.
@@ -225,6 +227,13 @@ private AIFunctionMcpServerTool(AIFunction function, Tool tool, IServiceProvider
         ProtocolTool = tool;
 
         _metadata = metadata;
+        _structuredContentSerializerOptions = tool.OutputSchema is not null &&
+            function.JsonSerializerOptions.DefaultIgnoreCondition is JsonIgnoreCondition.WhenWritingNull
+                ? new JsonSerializerOptions(function.JsonSerializerOptions)
+                {
+                    DefaultIgnoreCondition = JsonIgnoreCondition.Never,
+                }
+                : function.JsonSerializerOptions;
     }
 
     /// <inheritdoc />
@@ -677,7 +686,7 @@ private static void RewriteRefPointers(JsonNode? node)
             JsonElement jsonElement => jsonElement,
             JsonNode node => JsonSerializer.SerializeToElement(node, McpJsonUtilities.JsonContext.Default.JsonNode),
             null => null,
-            _ => JsonSerializer.SerializeToElement(aiFunctionResult, AIFunction.JsonSerializerOptions.GetTypeInfo(typeof(object))),
+            _ => JsonSerializer.SerializeToElement(aiFunctionResult, _structuredContentSerializerOptions.GetTypeInfo(typeof(object))),
         };
 
         // Pre-SEP-2106 clients expect the {"result": <value>} envelope for non-object
@@ -805,4 +814,4 @@ private static bool IsPrimitiveHeaderType(Type type)
                type == typeof(uint) ||
                type == typeof(long);
     }
-}
\ No newline at end of file
+}
diff --git a/tests/ModelContextProtocol.Tests/Server/McpServerToolTests.cs b/tests/ModelContextProtocol.Tests/Server/McpServerToolTests.cs
index 8fd1d9954..2a7a9af55 100644
--- a/tests/ModelContextProtocol.Tests/Server/McpServerToolTests.cs
+++ b/tests/ModelContextProtocol.Tests/Server/McpServerToolTests.cs
@@ -481,6 +481,58 @@ public async Task StructuredOutput_Enabled_ReturnsExpectedSchema<T>(T value)
         AssertMatchesJsonSchema(tool.ProtocolTool.OutputSchema.Value, result.StructuredContent);
     }
 
+    [Theory]
+    [InlineData(null, Sep2106ProtocolVersion)]
+    [InlineData("note", Sep2106ProtocolVersion)]
+    [InlineData(null, "2025-11-25")]
+    [InlineData("note", "2025-11-25")]
+    public async Task StructuredOutput_Enabled_RequiredNullableProperties_MatchesOutputSchema(string? note, string protocolVersion)
+    {
+        JsonSerializerOptions serializerOptions = new(McpJsonUtilities.DefaultOptions)
+        {
+            TypeInfoResolver = JsonTypeInfoResolver.Combine(
+                McpJsonUtilities.DefaultOptions.TypeInfoResolver,
+                new DefaultJsonTypeInfoResolver()),
+        };
+        McpServerTool tool = McpServerTool.Create(
+            () => new RequiredNullableOutput("42", note),
+            new() { Name = "tool", UseStructuredContent = true, SerializerOptions = serializerOptions });
+        var request = CreateRequestContextWithProtocolVersion(protocolVersion);
+
+        var result = await tool.InvokeAsync(request, TestContext.Current.CancellationToken);
+
+        Assert.NotNull(tool.ProtocolTool.OutputSchema);
+        Assert.NotNull(result.StructuredContent);
+        Assert.Equal(note is null ? JsonValueKind.Null : JsonValueKind.String, result.StructuredContent.Value.GetProperty("note").ValueKind);
+        AssertMatchesJsonSchema(tool.ProtocolTool.OutputSchema.Value, result.StructuredContent);
+    }
+
+    [Theory]
+    [InlineData(null, Sep2106ProtocolVersion)]
+    [InlineData("note", Sep2106ProtocolVersion)]
+    [InlineData(null, "2025-11-25")]
+    [InlineData("note", "2025-11-25")]
+    public async Task StructuredOutput_Enabled_RequiredNullablePropertiesInClass_MatchesOutputSchema(string? note, string protocolVersion)
+    {
+        JsonSerializerOptions serializerOptions = new(McpJsonUtilities.DefaultOptions)
+        {
+            TypeInfoResolver = JsonTypeInfoResolver.Combine(
+                McpJsonUtilities.DefaultOptions.TypeInfoResolver,
+                new DefaultJsonTypeInfoResolver()),
+        };
+        McpServerTool tool = McpServerTool.Create(
+            () => new RequiredNullablePropertiesOutput { Id = "42", Note = note },
+            new() { Name = "tool", UseStructuredContent = true, SerializerOptions = serializerOptions });
+        var request = CreateRequestContextWithProtocolVersion(protocolVersion);
+
+        var result = await tool.InvokeAsync(request, TestContext.Current.CancellationToken);
+
+        Assert.NotNull(tool.ProtocolTool.OutputSchema);
+        Assert.NotNull(result.StructuredContent);
+        Assert.Equal(note is null ? JsonValueKind.Null : JsonValueKind.String, result.StructuredContent.Value.GetProperty("note").ValueKind);
+        AssertMatchesJsonSchema(tool.ProtocolTool.OutputSchema.Value, result.StructuredContent);
+    }
+
     [Fact]
     public async Task StructuredOutput_Enabled_VoidReturningTools_ReturnsExpectedSchema()
     {
@@ -1091,6 +1143,15 @@ Instance JSON document does not match the specified schema.
 
     record Person(string Name, int Age);
 
+    private sealed record RequiredNullableOutput(string Id, string? Note);
+
+    private sealed class RequiredNullablePropertiesOutput
+    {
+        public required string Id { get; init; }
+
+        public required string? Note { get; init; }
+    }
+
     private static JsonSerializerOptions CreateSerializerOptionsWithPerson()
     {
         JsonSerializerOptions options = new(McpJsonUtilities.DefaultOptions);