As more and more Web services are deployed, Web service’s discovery mechanisms become essential. Similar services can have quite different QoS behaviors. For service selection and management purpose, it is necessary to clearly specify QoS constraints and metrics definitions for Web services. We investigate on the semantic QoS specification and introduce our design principles on it. Based on the specification refinement and conformance, we introduce the QoS matchmaking algorithm with multiple matching degrees. The matchmaking prototype is designed to prove the feasibility. Welldefined Metrics can be further utilized by measurement organizations to monitor and evaluate the promised service level objectives. Categories and Subject Descriptors H.3.5 [Online Information Services]: Web-based services; D.2.8 [Software Engineering]: Metrics-Performance measures General Terms Languages, Performance, Measurement Keywords Web Service Discovery, QoS, Semantic Web, Matchmaking