using System.Text.RegularExpressions;

using Newtonsoft.Json;

public class Program

{

    public static void Main()

    {

        string json = JsonConvert.SerializeObject(new SimpleClassWithRegex {RegProp = null}); 

        // json = {"RegProp":null}

        SimpleClassWithRegex obj = JsonConvert.DeserializeObject<SimpleClassWithRegex>(json); 

        //Above line throws a JsonSerializationException

    }

}

​

class SimpleClassWithRegex

{

    public Regex RegProp { get; set; }

}

​