The effects of territoriality on population density in the Japanese serow (Capricornis crispus) were investigated in Japan during 24 years, 1976–2000, on individually identified animals. Adult males and females defended intrasexual territories throughout the year. Few adults held no territory. The mean annual replacement rate of territories was 8.5% for females and 8.0% for males. The mating unit consisted of a monogamous pair (in 71.3% of units) and the polygynous unit (1 male with 2 females 25.0%; 1 male with 3 females 3.8%). The mean sex ratio (adult females : adult males) was 1:0.70. The mean ratio of adult females to offspring was 1:0.83. The population density was stable (mean ± SD; 14.2 ± 2.5/km²) through the study period. Adult density was negatively correlated with territory size in both sexes. We suggest that food availability controls adult density in the Japanese serow by influencing territory size.