The Service Oriented Architecture enables the development of flexible large scale-applications in open environments by dynamically combining Web services. Nevertheless, current techniques fail to address the problem of selecting adequate services to meet service consumer needs. Service selection must take into account non-functional parameters especially the Quality of Service (QoS). In this work we propose a Web service selection approach based on QoS attributes. We extend the WS-Policy to represent QoS policies. We apply ontological concepts to WS-policy in order to enable semantic matching. Publishing QoS policies is also examined in this work. We propose to extend the UDDI register to handle QoS-based policies.