I Want to return JSON webservice using Asp.net c#

Some more links -
JSON ASP.NET Web Services with jQuery[^]
How To Create A JSON Web Service In ASP.NET[^]
Returning JSON from a .Net 4.0 web service[^]

JSON is nothing more than a data exchange format delivered over string...
So if you have the method that creates the JSON in the server, all what you have to do is turn it into a string (stringify) and return it as a string from your method...

[WebMethod]
public string GetCargoInfo()
{
  return("{\"Cargo\":[...]}");
}

convert your json data to string and then in javascript convert the string to json


----Json.convert(string)
--------------------------------------------------------------------------------

public string json()
{

    JavaScriptSerializer a= new JavaScriptSerializer();
    var haha = new
    {
        nombre = "antonio",
        edad = 21
    };

    return a.Serialize ( new {result  = haha });

}

i think that, you should using WCF instantof Webservice
[ServiceContract]
public partial class BookmarkService
{
...
[WebInvoke(Method = "POST", RequestFormat=WebMessageFormat.Json,
UriTemplate = "users/{username}/bookmarks?format=json")]
[OperationContract]
void PostBookmarkAsJson(string username, Bookmark newValue)
{
HandlePostBookmark(username, newValue);
}
[WebGet(ResponseFormat= WebMessageFormat.Json,
UriTemplate = "users/{username}/bookmarks/{id}?format=json")]
[OperationContract]
Bookmark GetBookmarkAsJson(string username, string id)
{
HandleGetBookmark(username, id);
}
...
}

more detail here: https://msdn.microsoft.com/en-us/library/dd203052.aspx[^]

Check this article:
Web Service in ASP.NET (Return JSON and XML)