The diets of Lacerta vivipara and Rana temporaria were determined from the analysis of the stomach contents of individuals caught at the same time in the same place (Puy-de-Dôme, France). The diet of the common frog is more diversified, according to taxonomy as well as to the size of prey items. Besides, average length of prey captured by the frog (7.9 mm) is greater than that of the lizard (4.6 mm). Nevertheless the diet overlap index is much greater according to the later criterium than to taxonomic classification. Contrary to what has been shown in several cases where prey size is the main factor, trophic behaviour, hunting stratum and daily activity cycle- between others - play a great part in the separation of the trophic niches of the two studied populations. Finally, to evaluate the intensity of competition between the two species requires the determination of the availability of trophic resources as compared with the needs of predators.