Abstract: In this paper, a problem is studied, which evaluates XML queries using SQL statements in relational database systems. At first, an algorithm is proposed, which rewrites a regular path expression based XML query as a group of simple path expression based queries using mapping information（mapping graph）. A key problem in this process is that a Kleene expression cannot be rewritten using mapping graph directly. To handle this problem, statistical information of path instances is gathered to expand Kleene expressions. After that, an approach to rewrite a simple path expression into a SQL statement is described. The approaches presented are implemented in a virtual XML relational prototype system VXMLR. A preliminary performance study shows that the approaches are very effective.