An important source of palaeoecological and palaeoenvironmental information is intra-specimen variability of isotopic composition of mammal tooth enamel. It reflects seasonal or behavioral changes in diet and climate occurring during a life of the animal. While well-known in ungulates, in carnivorans this variability is poorly recognized. However, carnivoran remains are amongst the most numerous in the Pleistocene fossil record of terrestrial mammals, so their isotopic signature should be of particular interest. The aim of the study was to verify if enamel of a fossil cave hyena (Crocuta crocuta spelaea) and a cave bear (Ursus ingressus) records any regular inter- or intra-tooth isotopic variability. We examined intra-individual variability of δ13C and δ18O values in permanent cheek teeth enamel of fossil cave hyena and cave bear from the site of the Perspektywiczna Cave (southern Poland). We conclude that the isotopic variability of the cave hyena is low, possibly because enamel mineralization took place when the animals still relied on a uniform milk diet. Only the lowermost parts of P3 and P4 enamel record a shift toward an adult diet. In the case of the cave bear, the sequence of enamel formation records periodic isotopic changes, possibly correlating with the first seasons of the animal life.