The seasonal variation in home range size of one male and one female Iriomote Cat Prionailurus bengalensis iriomotensis was studied by radio-tracking and automatic photography on Iriomote Island, Japan. The study was conducted in the Shirahama area located in the western part of the island. Shirahama provides a small area of suitable lowland habitat (<50 m a.s.l.) for the Iriomote Cat. Two individuals, one male and one female, were confirmed to be resident in this area. The periodical home range size of the male was 1.24 ± 0.41 km² and that of the female was 1.30 ± 0.54 km² throughout the year, with no significant difference between them. We compared the results of these observations with those from another area of suitable habitat in Funaura and discussed what factors may affect male home range size. The home range of the male cat in Shirahama was found to be only half the size of that of males in Funaura, though it showed similar seasonal fluctuation. The home ranges of females were similar in the two areas. Our results provide empirical confirmation of the influence of the number and distribution of females on male home range size in a solitary felid.