Finding an edit script between data has played an important role in data retrieval and data transformation. So far many methods for finding an edit script between two XML documents have been proposed, but few studies on finding an edit script between an XML document and a DTD have been made. In this paper, we first present a polynomial-time algorithm for finding an edit script between an XML document and a DTD, which is optimum under some restrictions on operations. We next prove the correctness of the algorithm.