Nowadays, many different organizations which operate in the Web distributed environment become more and more dependent on services to automate their activities and to improve their interoperability. Services are provided and published on the Web by independent organizations and their number is growing. Therefore suitable approaches to classify and organize them to support their discovery and delivery are required. In this paper, we extend our ontologybased service classification and discovery approach to consider also the important and topical aspects related to QoS. In particular, in our approach services are firstly looked for on the basis of their functional conformance to the user request and then filtered on the basis of their quality features.