Growth and reproduction of the intertidal dotillid crab Ilyoplax deschampsi were studied in the Ariake Sea, Japan, and life history traits were compared with those of three other species of Ilyoplax occurring in temperate regions. New recruits of I. deschampsi occurred mainly in July and August, and their carapace widths (CW) were about 2 mm. They grew to 4 mm CW by December, and to 7 mm CW by the following July. Some crabs reached reproductive maturity in the second year of life, but others remained immature until the third year. Most crabs did not survive the third year. The main breeding season was from May to July, which ceased earlier than in other temperate species of Ilyoplax. Hepatic and ovarian weights were highest in early May and early June, respectively, and rapidly decreased after August. The earlier breeding of I. deschampsi is thought to be an adaptation for avoiding hot, dry habitat conditions during summer.