diff --git a/README.md b/README.md
index 2027d2b..d45b0ed 100644
--- a/README.md
+++ b/README.md
@@ -73,6 +73,17 @@ public partial class MyReactiveClass : ReactiveObject
 }
 ```
 
+### Usage Reactive property with set Access Modifier
+```csharp
+using ReactiveUI.SourceGenerators;
+
+public partial class MyReactiveClass : ReactiveObject
+{
+    [Reactive(SetModifier = AccessModifier.Protected)]
+    private string _myProperty;
+}
+```
+
 ## Usage ObservableAsPropertyHelper `[ObservableAsProperty]`
 
 ### Usage ObservableAsPropertyHelper with Field
diff --git a/src/ReactiveUI.SourceGenerators.Execute/TestViewModel.cs b/src/ReactiveUI.SourceGenerators.Execute/TestViewModel.cs
index e5cacd3..245e4c2 100644
--- a/src/ReactiveUI.SourceGenerators.Execute/TestViewModel.cs
+++ b/src/ReactiveUI.SourceGenerators.Execute/TestViewModel.cs
@@ -7,6 +7,7 @@
 using System.Reactive.Linq;
 using System.Runtime.Serialization;
 using System.Text.Json.Serialization;
+using System.Windows.Media.TextFormatting;
 using ReactiveUI;
 using ReactiveUI.SourceGenerators;
 
@@ -26,7 +27,7 @@ public partial class TestViewModel : ReactiveObject
     private double _test2Property = 1.1d;
 
     [JsonInclude]
-    [Reactive]
+    [Reactive(SetModifier = AccessModifier.Protected)]
     [DataMember]
     private int _test1Property = 10;
 
diff --git a/src/ReactiveUI.SourceGenerators.slnx b/src/ReactiveUI.SourceGenerators.slnx
index 4adf8d0..752cecd 100644
--- a/src/ReactiveUI.SourceGenerators.slnx
+++ b/src/ReactiveUI.SourceGenerators.slnx
@@ -23,6 +23,10 @@
     <Project Path="TestApps\TestMauiApplication\TestMauiApplication.csproj">
       <Deploy />
     </Project>
+    <Project Path="D:\Projects\GitHub\ReactiveUI\ReactiveUI.SourceGenerators\src\TestApps\TestAvaloniaApplication.Desktop\TestAvaloniaApplication.Desktop.csproj" />
+    <Project Path="D:\Projects\GitHub\ReactiveUI\ReactiveUI.SourceGenerators\src\TestApps\TestMauiApplication\TestMauiApplication.csproj">
+      <Deploy />
+    </Project>
   </Folder>
   <Properties Name="Visual Studio">
     <Property Name="OpenWith" Value="17" />
diff --git a/src/ReactiveUI.SourceGenerators/Core/Helpers/AttributeDefinitions.cs b/src/ReactiveUI.SourceGenerators/Core/Helpers/AttributeDefinitions.cs
index 8ae6dc2..3e4692d 100644
--- a/src/ReactiveUI.SourceGenerators/Core/Helpers/AttributeDefinitions.cs
+++ b/src/ReactiveUI.SourceGenerators/Core/Helpers/AttributeDefinitions.cs
@@ -12,6 +12,34 @@ internal static class AttributeDefinitions
     public const string GeneratedCode = "global::System.CodeDom.Compiler.GeneratedCode";
     public const string ExcludeFromCodeCoverage = "global::System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage";
     public const string Obsolete = "global::System.Obsolete";
+
+    public const string AccessModifierType = "ReactiveUI.SourceGenerators.AccessModifier";
+    public const string AccessModifierEnum =
+        """
+        // Copyright (c) 2024 .NET Foundation and Contributors. All rights reserved.
+        // Licensed to the .NET Foundation under one or more agreements.
+        // The .NET Foundation licenses this file to you under the MIT license.
+        // See the LICENSE file in the project root for full license information.
+        
+        // <auto-generated/>
+        #pragma warning disable
+        #nullable enable
+        namespace ReactiveUI.SourceGenerators;
+
+        /// <summary>
+        /// AccessModifier.
+        /// </summary>
+        internal enum AccessModifier
+        {
+            Public,
+            Protected,
+            Internal,
+            Private,
+            InternalProtected,
+            PrivateProtected,
+        }
+        """;
+
     public const string ReactiveObjectAttribute = """
 // Copyright (c) 2024 .NET Foundation and Contributors. All rights reserved.
 // Licensed to the .NET Foundation under one or more agreements.
@@ -90,7 +118,16 @@ namespace ReactiveUI.SourceGenerators;
 /// <seealso cref="Attribute" />
 [global::System.CodeDom.Compiler.GeneratedCode("ReactiveUI.SourceGenerators.ReactiveGenerator", "1.1.0.0")]
 [AttributeUsage(AttributeTargets.Field, AllowMultiple = false, Inherited = false)]
-internal sealed class ReactiveAttribute : Attribute;
+internal sealed class ReactiveAttribute : Attribute
+{
+    /// <summary>
+    /// Gets the AccessModifier of the set property.
+    /// </summary>
+    /// <value>
+    /// The AccessModifier of the set property.
+    /// </value>
+    public AccessModifier SetModifier { get; init; }
+}
 #nullable restore
 #pragma warning restore
 """;
diff --git a/src/ReactiveUI.SourceGenerators/ObservableAsProperty/ObservableAsPropertyGenerator.Execute.cs b/src/ReactiveUI.SourceGenerators/ObservableAsProperty/ObservableAsPropertyGenerator.Execute.cs
index af1d4b1..05617fa 100644
--- a/src/ReactiveUI.SourceGenerators/ObservableAsProperty/ObservableAsPropertyGenerator.Execute.cs
+++ b/src/ReactiveUI.SourceGenerators/ObservableAsProperty/ObservableAsPropertyGenerator.Execute.cs
@@ -272,7 +272,8 @@ internal static bool GetFieldInfoFromClass(
                 initializer,
                 isReferenceTypeOrUnconstraindTypeParameter,
                 includeMemberNotNullOnSetAccessor,
-                forwardedAttributes.ToImmutable());
+                forwardedAttributes.ToImmutable(),
+                "public");
 
             diagnostics = builder.ToImmutable();
 
diff --git a/src/ReactiveUI.SourceGenerators/Reactive/Models/PropertyInfo.cs b/src/ReactiveUI.SourceGenerators/Reactive/Models/PropertyInfo.cs
index c39ba59..500e933 100644
--- a/src/ReactiveUI.SourceGenerators/Reactive/Models/PropertyInfo.cs
+++ b/src/ReactiveUI.SourceGenerators/Reactive/Models/PropertyInfo.cs
@@ -3,6 +3,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for full license information.
 
+using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using ReactiveUI.SourceGenerators.Helpers;
 
@@ -18,4 +19,5 @@ internal sealed record PropertyInfo(
     EqualsValueClauseSyntax? Initializer,
     bool IsReferenceTypeOrUnconstraindTypeParameter,
     bool IncludeMemberNotNullOnSetAccessor,
-    EquatableArray<AttributeInfo> ForwardedAttributes);
+    EquatableArray<AttributeInfo> ForwardedAttributes,
+    string AccessModifier);
diff --git a/src/ReactiveUI.SourceGenerators/Reactive/ReactiveGenerator.Execute.cs b/src/ReactiveUI.SourceGenerators/Reactive/ReactiveGenerator.Execute.cs
index 35cd2c8..8d024d8 100644
--- a/src/ReactiveUI.SourceGenerators/Reactive/ReactiveGenerator.Execute.cs
+++ b/src/ReactiveUI.SourceGenerators/Reactive/ReactiveGenerator.Execute.cs
@@ -80,10 +80,22 @@ internal static MemberDeclarationSyntax GetPropertySyntax(PropertyInfo propertyI
                         setterFieldExpression,
                         IdentifierName("value"))));
 
+            SyntaxToken[] syntaxKinds = propertyInfo.AccessModifier switch
+            {
+                "public" => [],
+                "protected" => [Token(SyntaxKind.ProtectedKeyword)],
+                "internal" => [Token(SyntaxKind.InternalKeyword)],
+                "private" => [Token(SyntaxKind.PrivateKeyword)],
+                "internal protected" => [Token(SyntaxKind.InternalKeyword), Token(SyntaxKind.ProtectedKeyword)],
+                "private protected" => [Token(SyntaxKind.PrivateKeyword), Token(SyntaxKind.ProtectedKeyword)],
+                _ => [],
+            };
+
             // Create the setter for the generated property:
-            //
+            // Literal(propertyInfo.AccessModifier)
             // set => this.RaiseAndSetIfChanged(ref <FIELD_NAME>, value);
             var setAccessor = AccessorDeclaration(SyntaxKind.SetAccessorDeclaration)
+                .AddModifiers(syntaxKinds)
                 .WithExpressionBody(ArrowExpressionClause(ParseExpression($"this.RaiseAndSetIfChanged(ref {getterFieldIdentifierName}, {IdentifierName("value")});")));
 
             // Add the [MemberNotNull] attribute if needed:
@@ -168,6 +180,29 @@ internal static bool GetFieldInfoFromClass(
             var propertyName = GetGeneratedPropertyName(fieldSymbol);
             var initializer = fieldSyntax.Declaration.Variables.FirstOrDefault()?.Initializer;
 
+            if (!fieldSymbol.TryGetAttributeWithFullyQualifiedMetadataName(AttributeDefinitions.ReactiveAttributeType, out var attributeData1))
+            {
+                propertyInfo = null;
+                diagnostics = builder.ToImmutable();
+
+                return false;
+            }
+
+            token.ThrowIfCancellationRequested();
+
+            // Get AccessModifier enum value from the attribute
+            attributeData1.TryGetNamedArgument("SetModifier", out int? accessModifierArgument);
+            var accessModifier = accessModifierArgument switch
+            {
+                0 => "public",
+                1 => "protected",
+                2 => "internal",
+                3 => "private",
+                4 => "internal protected",
+                5 => "private protected",
+                _ => "public",
+            };
+
             // Check for name collisions
             if (fieldName == propertyName)
             {
@@ -298,7 +333,8 @@ internal static bool GetFieldInfoFromClass(
                 initializer,
                 isReferenceTypeOrUnconstraindTypeParameter,
                 includeMemberNotNullOnSetAccessor,
-                forwardedAttributes.ToImmutable());
+                forwardedAttributes.ToImmutable(),
+                accessModifier);
 
             diagnostics = builder.ToImmutable();
 
diff --git a/src/ReactiveUI.SourceGenerators/Reactive/ReactiveGenerator.cs b/src/ReactiveUI.SourceGenerators/Reactive/ReactiveGenerator.cs
index 382a62d..252fad9 100644
--- a/src/ReactiveUI.SourceGenerators/Reactive/ReactiveGenerator.cs
+++ b/src/ReactiveUI.SourceGenerators/Reactive/ReactiveGenerator.cs
@@ -27,7 +27,13 @@ public sealed partial class ReactiveGenerator : IIncrementalGenerator
     public void Initialize(IncrementalGeneratorInitializationContext context)
     {
         context.RegisterPostInitializationOutput(ctx =>
-            ctx.AddSource($"{AttributeDefinitions.ReactiveAttributeType}.g.cs", SourceText.From(AttributeDefinitions.ReactiveAttribute, Encoding.UTF8)));
+        {
+            // Add the AccessModifier enum to the compilation
+            ctx.AddSource($"{AttributeDefinitions.AccessModifierType}.g.cs", SourceText.From(AttributeDefinitions.AccessModifierEnum, Encoding.UTF8));
+
+            // Add the ReactiveAttribute to the compilation
+            ctx.AddSource($"{AttributeDefinitions.ReactiveAttributeType}.g.cs", SourceText.From(AttributeDefinitions.ReactiveAttribute, Encoding.UTF8));
+        });
 
         // Gather info for all annotated command methods (starting from method declarations with at least one attribute)
         IncrementalValuesProvider<(HierarchyInfo Hierarchy, Result<PropertyInfo> Info)> propertyInfoWithErrors =