Roe deer feeding habits were studied in the western Alps during the summer season using the faecal analysis method. The diet of cattle grazing in the same area was also investigated and the trophical niche overlap between the two species was determined. The roe deer diet was found very variable and mostly composed of dicotyledons, with Leguminosae and Cistaceae as prevalent species. Monocotyledons, mainly represented by Graminaceae, were consumed to a lesser extent. A significant preference was observed for Cistaceae and other dicotyledons whereas a significant refuse was observed for Graminaceae and Asteraceae. These data confirmed the roe deer's behaviour to select food with a better nutritive value. Despite the differences between the cattle and roe deer's diets, the trophical niche overlap was quite high. This can be explained by the homogeneity of the plants covering the whole area which probably limited food selection by the roe deer.