Dietary composition, fecal crude protein, plant fragment sizes, and their fragmentation processes through the digestive tract were compared for sika deer and Japanese serow in northern Japan. Dwarf bamboo and graminoids were important food plants for sika deer, whereas dicotyledonous leaves, particularly those of evergreen shrubs, were important for Japanese serow. Fecal crude protein was always higher and fecal plant fragments were smaller in Japanese serow than in sika deer. Japanese serow digested plants better and fragmented plant material through the digestive tract more markedly than did sika deer. Two interpretations are possible: smaller fragments in serow feces resulted from 1) differences in food availability in the habitats, or 2) differences in digestive physiology of the two ungulates. Although this study suggests the latter interpretation, more studies of sympatric populations are needed.