C#

string xml = string.Empty;
System.Xml.XmlWriterSettings settings = new System.Xml.XmlWriterSettings();
StringWriter sw = new StringWriter();
settings.OmitXmlDeclaration = true;
XmlSerializerNamespaces ns = new XmlSerializerNamespaces();
ns.Add("", "");
using (System.Xml.XmlWriter writer = System.Xml.XmlWriter.Create(sw, settings))
{
    XmlSerializer ser = new XmlSerializer(typeof(Content));
    ser.Serialize(writer, this, ns);
    return sw.ToString();
}

Type 'System.Xml.XmlNode' in Assembly 'System.Xml, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' is not marked as serializable

[Serializable]
[DataObject(true)]
public  class Content : ISerializable
{
  //Constructors
    public Content() { }
    public Content(SerializationInfo info, StreamingContext context)
    {
        this.contentCollection = (List<Content> )info.GetValue("ContentCollection", typeof(List<Content> ));
        this.ContentId = info.GetInt64("ContentId");
        this.Name = info.GetString("Name");
        this.Owner = (Owner)info.GetValue("Owner", typeof(Owner));
    }

  //Properties
    private List<Content> contentCollection;
    [XmlArray("ContentCollection")]
    public List<content> ContentCollection
    {
        get
        {
            if (contentCollection == null) contentCollection = new List<content>();
            return this.contentCollection;
        }
    }

    private System.Int64 contentIdField;
    [XmlAttribute("ContentId")]
    public System.Int64 ContentId
    {
        get { return this.contentIdField; }
        set { this.contentIdField = value; }
    }

    private System.String nameField;
    [XmlElement("Name")]
    public System.String Name
    {
        get { return this.nameField; }
        set { this.nameField = value; }
    }

    private Owner owner;
    [XmlElement("Owner")]
    public Owner Owner
    {
        get { return this.owner; }
        set { this.owner = value; }
    }

    //Deserialization
    #region ISerializable Members
    public void GetObjectData(SerializationInfo info, StreamingContext context)
    {
        info.AddValue("ContentCollection", this.ContentCollection);
        info.AddValue("ContentId", this.ContentId);
        info.AddValue("Name", this.Name);
        info.AddValue("Owner", this.Owner);
    }
    #endregion</content></content>

[Serializable]
[DataObject(true)]
public class Owner : ISerializable
{
    //Constructors
    public Owner() { }
    public Owner(SerializationInfo info, StreamingContext context)
    {
        this.OwnerId = info.GetInt64("OwnerId");
    }

    //Properties
    private long ownerId;
    [Browsable(false)]
    [XmlAttribute("OwnerId")]
    public long OwnerId
    {
        get { return ownerId; }
        set { ownerId = value; }
    }

    #region ISerializable Members
    public void GetObjectData(SerializationInfo info, StreamingContext context)
    {
        info.AddValue("OwnerId", this.ownerId);
    }

    #endregion
}