To identify the dietary composition and characteristics of both Adélie (Pygoscelis adeliae) and emperor penguin (Aptenodytes forsteri) at four breeding sites, we performed stable carbon (δ13C) and nitrogen (δ15N) isotope analysis of down of penguin chicks. Adélie penguin chicks at Cape Hallett mostly fed on Antarctic krill (Eupausia superba; 65.5±3.5%) reflecting the prevalence of that species near Cape Hallett, and no significant differences were noted between 2017 and 2018. However Adélie penguin chicks at Inexpressible Island located near Terra Nova Bay fed on both Antarctic silverfish (Pleuragramma antarctica; 42.5%) and ice krill (Euphausia crystallorophias; 47%) reflecting the high biomass observed in Terra Nova Bay. On the other hand, no significant difference was noted between at both breeding sites of the emperor penguin. Emperor penguin chicks predominantly fed on Antarctic silverfish (74.5±2.1%) at the breeding sites (Cape Washington and Coulman Island), suggesting that diet preference represents the main factor for emperor penguin foraging. In contrast, the diet of Adélie penguin reflected presumed regional differences in prey prevalence as inferred from available survey data.