We examined food habits and home-range elevations of Japanese black bears (Ursus thibetanus japonicus) in relation to Fagaceae mast production in Toyama Prefecture. Nine bears (four males and five females) fitted with GPS collars were tracked for various periods from July to December in 2005–2007. We investigated the food habits of each bear using traces found at GPS-fix locations. Bears selectively fed on Fagus crenata mast when F. crenata and Quercus crispula mast was abundant and consumed Q. crispula and Q. serrata mast when F. crenata mast was scarce. When both F. crenata and Q. crispula mast was scarce, bears fed on multiple alternatives, such as Diospyros kaki. Home-range elevations of bears also differed among years in response to vertical distributions of available foods. Individual bears captured in the Q. serrata zone (lower elevation) and F. crenata zone (higher elevation) tended to eat Q. serrata and Q. crispula acorns, respectively, when F. crenata mast was not available. Therefore, food habits and home-range elevations of bears were influenced greatly by fluctuations in Fagaceae mast production and the species' vertical distribution, as well as by factors such as food preference for F. crenata mast and food resource distribution around the home ranges.