We examined the relationship between the feeding habits of Asian black bears (Ursus thibetanus) and fruit availability during summer and autumn from 2008 to 2011 in the Ashio-Nikko Mountains, Japan. Our main questions were as follows: 1) How does the availability of multiple fruit species influence the feeding habits during summer and autumn? and 2) When do bears begin to forage on hard mast in relation to the availability of various fruit species during summer and autumn? The relationship between feeding habits and fruit availability differed between seasons: in summer, bears ate any fruit species that was available, whereas in autumn, Quercus crispula was the first fruit used, even in poor masting years when other fruit species were more available. In addition, the time when bears started to consume Q. crispula differed between years; more than half a month earlier in years when Padus grayana, the main food item prior to Q. crispula in this area, was not available. Thus, the timing of presence of prior foods may influence the timing of food transition. This demonstrates that both the abundance and timing of fruiting influence the feeding habits of bears.