On one part, the paper presents a phenomenological description allowing the simulation of the mechanical behaviour of shape memory alloys (SMA). Our theoretical work is focused on the pseudoelasticity related to the creation of the martensite phase from the mother phase (austenite). An isothermal tensile loading is performed here to induce this phase transformation. The thermodynamics of irreversible processes framework was used. One internal variable is taken into account : the volume fraction of martensite produced under stress action. On another part, Ti-Ni shape memory thin films are made by r.f. magnetron sputtering. Tensile tests are performed at various temperatures. The parameters of the model have been identified for two particular SMA (Ti-48.0 at.% Ni and Ti-50.3 at.% Ni) and the simulated results show good agreements with experiments.