List<Customer> lst = new List<Customer>();
Customer c = new Customer();
c.ID = 1;
c.Name = "one";
lst.Add(c);

c = new Customer();
c.ID = 2;
c.Name = "tow";
lst.Add(c);

XmlDocument xd = new XmlDocument();
using (StringWriter sw = new StringWriter())
{
    XmlSerializer xz = new XmlSerializer(lst.GetType());
    xz.Serialize(sw, lst);
    Console.WriteLine(sw.ToString());
    xd.LoadXml(sw.ToString());
    xd.Save("c://1.xml");
}

List<Customer> lst2 = new List<Customer>();
using (XmlReader reader = XmlReader.Create("c://1.xml"))
{
    XmlSerializer xz = new XmlSerializer(lst2.GetType());
    lst2=(List<Customer>)xz.Deserialize(reader);
    Console.WriteLine(reader.ToString());
}