H, C, N, O stable isotope ratios of forage, milk and the corresponding cheese were analysed to define the isotopic characteristics of two typical mountain cheeses produced in two different terroirs with different types of vegetation. δ13C was shown to be mainly influenced by the presence of C4 plants in animal diet and, in the case of C3 plant-based forage it was below −23‰ varying according to the site and herbage type. δ15N is more related to vegetation type and confirmed to be lower than +4‰ for alpine products. The altitude of the origin area influences δ18O and δ2H. The isotopic values of milk and cheese casein were not significantly different, except δ18O, while they were both significantly different from the values of forage, except δ2H. Using the combined stable isotope ratios a good discrimination level between the products from two different types of pasture at two mountain sites was achieved.