How XML is applied to the digital library systems is introduced in this paper. The major features of XML are reviewed and compared with those of HTML.The subsystem of the Korean Virtual Library and Information System(VINIS)，an experimental XMLbased metadata retrieval system is demonstrated here. This subsystem consists of two modules: a retrieval module and a browsing module. The retrieval module allows the retrieval of metadata stored in Microsoft access files and the display of search result in a XML file format. The browsing module allows browsing of metadata in XMUXSL file format. Finally, the way how XML will be more efficiently applied in digital libraries is discussed.