To assess the degree of competition for food items between non-natives and natives, dietary overlap among three carnivore species living sympatrically in the area of Isumi City, southeastern Chiba Prefecture, central Japan, was analyzed by examining the gut contents of 221 animals collected from spring through summer 2006. The animals comprised two introduced species, the raccoon Procyon lotor and the masked palm civet Paguma larvata, and a native species, the raccoon dog Nyctereutes procyonoides. All three species were found to eat berries and seeds, amphibians and arthropods. The raccoons ate more crustaceans, the masked palm civets ate more mollusks, and the raccoon dogs ate more human meal scraps than the other two species. The food diversity of raccoons was lowest in both spring and summer. The dietary overlap was highest between raccoon dogs and masked palm civets. The degree of dietary overlap among the three species increased from spring to summer. These results suggest that overlap of food items is high and the degree of food resource segregation is low among the three species.