This work deals with the preparation and the characterization of palladium and palladium-molybdenum supported on HY and NaY zeolites, with the aim to study the effect of molybdenum on the properties of palladium. Catalytic performances were tested in the reaction of methane combustion. The introduction of molybdenum in palladium exchanged zeolites NaY and HY was realized in dynamic or static regime (under vacuum) using Mo(CO) 6 vapor at ambient temperature. Pd was found to migrate in supercages under the influence of Mo(CO) 6 , which produces by decomposition, Mo 5 + species revealed by EPR spectroscopy and consequently palladium was reduced. Catalytic results show that the activity of PdHY increases with time during a relatively long period compared to the other samples. This activation in stream can be attributed to a slow migration of palladium to supercages. Nevertheless, PdHY and PdMoNaY were less active than PdNaY at 500 o C. The catalytic activity of monometallic samples increases with time, whereas it decreases for bimetallic ones. The comparison of the catalytic activities of Pd and Pd Mo supported on NaY and HY suggests that the basicity of the support enhances the oxidation ability of palladium by an increase of the electronic density of the metal particles at the surface. The pretreatment conditions exerted also a great effect on the behavior of mono and bimetallic catalysts. The reduction in hydrogen at 500 o C led to a decrease of the combustion activity depending on the nature of the catalyst.