Non-functional requirements are especially critical in real-time and distributed systems. UML is progressively becoming a standard of object- oriented analysis and design of systems, it pays attention to software architec- tures specification, but it does not take into account their evaluation, and the specification of resource restrictions and non-functional requirements. In this paper we introduce an approach for the evaluation of non-functional require- ments in UML models, using simulation techniques. Simulation models are generated automatically, and their execution provides results to evaluate the UML architectures. The simulation statistics generated allow the evaluation of some non-functional requirements like resources usage, objects and classes ac- tivity and availability, restoration times of errors and throughputs. We associate these results to objects, classes, states, operations, actors, system resources and other UML elements. UML semiformal semantics have associated problems that we reduce with UML extension techniques.