How to serialize an object to XML without getting xsi and xsd

To remove namespaces all together

just add

var ns = new XmlSerializerNamespaces();
ns.Add("", "");

and then

var xmlSerializer = new XmlSerializer(typeof(Project));

xmlSerializer.Serialize(fs, project, ns);

but if you want to keep xmlns only with xsi and xsd you should add default namespace to XmlSerializer like this

var defaultNamespace = "http://schemas.microsoft.com/developer/msbuild/003";
var xmlSerializer = new XmlSerializer(typeof(Project), defaultNamespace);
 
xmlSerializer.Serialize(fs, project, ns);