I am having trouble sending JavaScript objects as a http request that only accepts json content-type. i.e "application/json" or "text/json" But, I am not sure why data2 ( stringified json ) works fine But, data1 ( json object ) does throws 400 ( Bad Request ). i.e I am not sure jQuery does not serialize the json object to a valid json string for the server to process. var data1 = ({ rating : 3 }); //does not work var data2 = '{ "rating" : 3}'; //works fine $.ajax({ url : "/rate", data : data1, type : "POST", contentType: "application/json", success: function(json){ console.log("Ajax Return :"+json); } });