The mammalian fauna of five new fossiliferous occurences of Upper Oligocene age is described in detail. This mammalian fauna, which consists mainly of Rodents, belong for the most part to the "Marnes grises à gypse" (Gray gypsiferous marls) of western Switzerland. This formation had previously yielded only very few mammalian fossils. The comparison with several type-occurences in France, South Germany and Switzerland is discussed.