The enormous web documents in WWW have made it dramatically difficult to retrieve meaningful information which we really want to find out. The Semantic Web technology has been considered to solve the problem and RDF and OWL have emerged as standards for the Semantic Web documents by W3C. The RDF/XML, an XML representation of RDF and OWL, documents are very large as compared to their intrinsic data size because of their inherent verbosity from XML. These large-size RDF/XML documents are inefficient in data exchanging and archiving. In this paper, we propose an efficient method for compressing URI references which may cover very large portions of RDF/XML documents. Our compression method compresses URI references using two-level dictionary-based encoding: one for compressing URI parts of URI references and the other for compressing whole URI references. The performance evaluation using real RDF/XML documents shows that our compression method significantly reduces the size of the RDF/XML documents.