The aim of the work presented in this paper is to introduce a method for verifying temporal requirements of time-constrained systems. The method allows the automated veri cation of temporal require- ments, initially expressed in a semi-formal formalism, through model transformation and model-checking. For the several advantages it o ers, UML has been used for the rst-step speci cation translated thereafter into a formal speci cation. Concretely, the input model for the transformation is an UML State Machines (SM) depicting the system temporal requirements. SM has a rich semantics and o ers big exibility. On the other hand, Timed Automata has proven to be useful for verifying temporal constraints and several veri cation tools are based on this formal notation. The rst contribution of this paper consists of developing an algorithm for transforming UML SM with time annotations into Timed Automata. Once the temporal requirements of the studied system are speci ed, the veri cation is proceeded on the basis of some observation patterns we have developed. The global approach is illustrated through the level crossing case study.