POST request json

Try the below code

    +(NSData *)postDataToUrl:(NSString*)urlString:(NSString*)jsonString
    {
        NSData* responseData = nil;
        NSURL *url=[NSURL URLWithString:[urlString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]];
        responseData = [NSMutableData data] ;
        NSMutableURLRequest *request=[NSMutableURLRequest requestWithURL:url];
        NSString *bodydata=[NSString stringWithFormat:@"data=%@",jsonString];

        [request setHTTPMethod:@"POST"];
        NSData *req=[NSData dataWithBytes:[bodydata UTF8String] length:[bodydata length]];
        [request setHTTPBody:req];
        NSURLResponse* response;
        NSError* error = nil;
        responseData = [NSURLConnection sendSynchronousRequest:request     returningResponse:&response error:&error];
        NSString *responseString = [[NSString alloc] initWithData:responseData encoding:NSUTF8StringEncoding];

        NSLog(@"the final output is:%@",responseString);

        return responseData;
    }

Ref: http://stackoverflow.com/questions/5537297/ios-how-to-perform-an-http-post-request