In this paper we present the results of the XPS atomic depth profile analysis, using ion beam sputtering, of L-CVD SnO2 thin films grown on an atomically clean SiO2 substrate after annealing at 400 °C in dry atmospheric air. From the evolution of the Sn 3d5/2, O 1s, Si 2p and C 1s core level peaks our experiments allowed the determination of the in depth atomic concentration of the main components of the SnO2/SiO2 interface. Thin (few nm) nearly stoichiometric SnO2 films are present at the topmost layer of the thin films, and progressive intermixing with SnO and silicon oxide is observed at deeper layer. The interface between the Sn and the Si oxide layers (i.e. the effective Sn oxide thickness) is measured at 13 nm.