This paper proposes an Ontology-based Rights Expression Language, called OREL. Based on OWL Web Ontology Language, OREL allows not only users but also machines to handle digital rights at semantics level. The ontology-based rights model of OREL is also presented. The usage of OREL and its advantages against existing RELs are discussed. Categories and Subject Descriptors K.4.1 [Public Policy Issues]: Intellectual property rights; I.2.4 [Knowledge Representation Formalisms and Methods]: Representation languages. General Terms Languages, Security, Standardization. Keywords Rights Expression Language, XrML, OWL, OREL.