A DTD or XML Schema in its current textual form commonly lacks clarity and readability, therefore erroneous, poor quality design and usage are inevitable. A canonical conceptual model for XML documents will provide an effective mean of designing XML documents. The DTD is an early standard for XML and used in legacy systems widely. This paper presents an approach for converting a DTD to a conceptual model. By using the conceptual model, users can restructure the existed XML documnets, improve its quality, and integrate various XML documents. In our approach, the conceptual model is represented using standard UML class notation, annotated with a few additional constraints, and the care of the converting process is a set of transformation rules that consider not only the DTD structure but also its semantics in order to generate the corresponding elements, especially, the inheritance structure can be extracted from the DTD structure.