Get child from root
import org.jdom.Document; import org.jdom.Element; import org.jdom.input.SAXBuilder; import org.jdom.output.Format; import org.jdom.output.XMLOutputter; public class MainClass { public static void main(String[] args) throws Exception { SAXBuilder builder = new SAXBuilder(); Document books = builder.build("books.xml"); Document onebook = builder.build("onebook.xml"); Element bookToAdd = onebook.getRootElement().getChild("book"); books.getRootElement().addContent(bookToAdd); new XMLOutputter(Format.getPrettyFormat()).output(books, System.out); } }