This paper presents the QoS-MO ontology. This ontology enables the specification of QoS requirements for Semantic Web Services and can easily be combined with OWL-S in order to fully describe Web Services. The QoS specifications created using the QoS-MO ontology may be employed on the design and development of Web Services and on the publication and discovery of Web Services on the Semantic Web. Categories and Subject Descriptors D.2.12 [Software Engineering]: Interoperability