The diets of the wolf Canis lupus, red fox Vulpes vulpes and raccoon dog Nyctereutes ussurienusis Matschie were studied in the grassland of eastern Inner Mongolia from August to October in 2007 and from March to July in 2008. Feces were collected from dens and latrines. The frequency of occurrence and the dry weight of the remains of each food item in the feces were calculated. Livestock (50.65% frequency of occurrence) constituted the bulk of the wolf diet, while small rodents (76.31% frequency of occurrence) were most frequently eaten by the foxes. Small rodents (22.69% frequency of occurrence) were important to the raccoon dogs but they also frequently consumed birds (39.81% frequency of occurrence) and insects (26.39% frequency of occurrence). The wolf was the most omnivorous and the red fox was the least omnivorous of these three kinds of canidae according to the diversity index. The food niches of the wolf and the red fox overlapped more than that of the raccoon dog and other species. These three kinds of canidae shared many resources and consequently competition occurred to them. However, their diets also differed to some extent which helped them to avoid competition. Furthermore, raccoon dogs were dormant in winter when food was scarce, which may be the reason why all these species could coexist in a rather unproductive grassland.