Nowadays, semantic integration of data resources is becoming a hot topic. Many techniques have been developed to map XML sources to ontologies, but most of mapping processes are manually accomplished with the help of experts. In this paper, we propose a new method that automatically derives such mappings by using DTD information, i.e. mappings XML fragments to concepts and roles in ontologies. Our algorithm can deal with structural difference between XML documents and ontologies by matching DTD structure with ontology graphs, and then automatically generates the mapping rules in XPath of DTD to the conceptual paths in the ontology. The whole process is automatic with little human intervention, in this way multifarious information integration will become much easier.