NonSerializedAttribute

NonSerializedAttribute is a .NET attribute used to mark a field of a serializable class to be excluded from serialization when using the BinaryFormatter. It resides in the System namespace as NonSerializedAttribute and is used by applying the short form [NonSerialized] on a field inside a [Serializable] class. It targets fields and does not apply to properties.

During serialization with BinaryFormatter, any field marked with NonSerializedAttribute is not written to the serialized stream. Upon deserialization, that field is initialized to its default value for the field's type, meaning reference types become null, value types become zero-equivalent, and booleans become false. This makes it suitable for fields that hold transient data, caches, or sensitive information that should not be persisted.

The attribute's effect is limited to BinaryFormatter-like serializers that honor it. Other serializers, such as DataContractSerializer, XmlSerializer, or JSON serializers, do not rely on NonSerializedAttribute and have their own mechanisms for ignoring members. In modern .NET usage, BinaryFormatter is considered unsafe and is obsolete; you should avoid relying on NonSerializedAttribute for security or long-term persistence, and instead use appropriate serialization options for the target serializer, or refactor design to exclude sensitive data from serialization.

Declaration: [AttributeUsage(AttributeTargets.Field, Inherited = false)] public sealed class NonSerializedAttribute : Attribute. The attribute's short name is NonSerialized.