asp.net web forms json return result

Return the list instead, and use [ScriptMethod(ResponseFormat = ResponseFormat.Json)] attribute – it will create JSON object as return automatically:

[WebMethod]
[ScriptMethod(ResponseFormat = ResponseFormat.Json)] 
public List<RetUsers> GetSomething()
{
  // avoid circual reference(parent child)
  List<RetUsers> res = repo.GetAllUser().Select(c => new RetUsers {User_ID = c.User_ID,User_Name = c.User_Name,Date_Expire = c.Date_Expire }).ToList();

  return res;
}

And on JS side:

$.ajax(
{
    type: "POST",
async: true,
url: YourMethodUrl,
data: {some data},
contentType: "application/json; charset=utf-8",
dataType: "json",
    success: function(msg)
    {
        var resultAsJson = msg.d // your return result is JS array
        // Now you can loop over the array to get each object
        for(var i in resultAsJson)
        {
            var user = resultAsJson[i]
            var user_name = user.User_Name
            // Here you append that value to your label
        }
    }
})