using System;

using Newtonsoft.Json;

public class Program

{

    public static void Main()

    {

        Foo foo = new Foo { Date = new DateTime(2009,06,04,3,0,0) };

        JsonSerializerSettings settings = new JsonSerializerSettings

        {

            DateFormatHandling = DateFormatHandling.MicrosoftDateFormat,

            Formatting = Formatting.Indented

        };

        string json = JsonConvert.SerializeObject(foo, settings);

        Console.WriteLine(json);

    }

}

​

class Foo

{

    public DateTime Date { get; set; }

}