New amorphous molybdenum oxysulfide thin films have been obtained by RF sputtering under oxygen partial pressure. The lithium intercalation process in these materials depends on their composition. Up to 3.5 mole lithium per mole molybdenum can be intercalated in the films with high oxygen content, 1.7 in the others. The intercalation of the first lithium is never reversible. The evolution of the derivative of incremental capacity curves as a function of cell voltage can partially explain the oxidation-reduction mechanisms. The lithium diffusion coefficient has been determined with Honders’ method and found equal to 10(-13)cm(2) s(-1) at the beginning of the intercalation.