In this paper a study about the effect of the Ga addition to Pt/Al2O3 on the performance in propane dehydrogenation is reported. Mono and bimetallic catalysts were characterized by tests reactions, TPR, H-2 chemisorption, FT-IR of preadsorbed CO, and tested in propane dehydrogenation by using a pulse technique. Results showed that the selectivity to propylene is enhanced by the Ga addition, while the catalyst deactivation and the carbon formation are decreased when the Ga content increased. Ga appears to have a very low effect on the acidity function, but it modifies the structure of the metallic phase in a different way according to the previous reduction temperature. Thus, at low reduction temperature (573 K) the action of Ga can be related only to geometric effects, while after reducing at high temperature (773 K), additional effects including Ga blocking, and in a minor extension, an electronic modification of Pt sites, would take place.