We propose a cache management method of XML Databases in this research. XQuery is the most popular XML query language in XML Databases. The tree-structured XML data can be traversed along XPath expressions used in part of XQuery. Two XPath expressions being compared, the containment relationship of these results could be judged. In this work, we pay attention to the relationship and propose a method of cache management using it as meta information when doing the cache replacement. Although the cache management by the unit of page or tuple was a main technique in the relational databases, the merit and demerit of doing the cache management by the unit of query in the XUL databmes are discussed in this paper.