Add namespace to attribute
using System; using System.IO; using System.Xml; using System.Xml.Linq; using System.Collections; using System.Collections.Generic; public class MainClass{ public static void Main(){ XNamespace aw = "http://www.domain.com"; XElement root = new XElement(aw + "Root", new XAttribute(XNamespace.Xmlns + "aw", "http://www.domain.com"), "Content"); Console.WriteLine(root); } }