An analytical Green's function approach to the study of the electrical transport in bimetallic films is presented. Taking into account the quantum size effects and considering three types of scattering from bulk impurities, rough surfaces and a rough interface, we calculate the one-partical Green's functions and the in-plane conductivity, yielding a new formula for conductivity in bimetallic films. It is found that in the thin-film limit and to the lowest order in the surface and interface scattering, the total conductivity is given by a sum of conductivities of all the subbands and for each subband the scattering rates due to the impurities, surfaces and interface are additive.