We monitored the food habits of sika deer in western mountain areas of Tokyo, Japan from the winter of 2001 to the summer of 2010. The items of the diets were divided into green broad leaves, dead broad leaves, coniferous leaves, forbs, graminoids, sasa group, seed related parts, trunk bark, and others including twigs, ferns, lower plants, mushroom, and unidentified materials. The food habits of sika deer showed obvious seasonal variations in all diets parts. Contrary to green broad leaves and forbs, the proportion of dead broad leaves and sasa changed from 1.4% and 1.4% in spring or summer to 54.3% and 26.4% in winter respectively. Coniferous leaves and truck barks were used mainly in winter.