Abstract: The normalization problem of XML DTD is studied XML documents may contain redundant information and operation anomalies due to a bad designed DTD which implies the similar dependencies among elements and attributes just as in relational database schemas The concept of multi valued dependency for XML DTD is proposed And then XNF, an XML normal form, is defined based on the concept of multi valued dependency The concept of lossless join decomposition for DTD is defined by the relational representation of DTD Finally, a lossless join decomposition algorithm for transforming a DTD into XNF is given