Bull. Jpn. Soc. Fish. Oceanogr. 71(1), Page 29-37, 2007   Spawning ground of marbled sole Pleuronectes yokohamae in the northern part of Harima Nada, the Seto Inland Sea, Japan Minoru Tanda†1 and Ryuichi Nagai2 1 Fisheries Technology Institute, Hyogo Prefectural Technology Center for Agriculture, Forestry and Fisheries, Akashi, Hyogo 674-0093, Japan 2 Japan Marine Ecology Institute Co., Ltd., Toyonaka, Osaka 561-0808, Japan †e-mail: minoru_tanda@pref.hyogo.jp We investigated spawning ground habitats of marbled sole Pleuronectes yokohamae in the northern part of Harima Nada, the Seto Inland Sea, using scuba-diving in an area where mature fish were caught, in winter of 2000 and 2001. A large number of eggs spawned by marbled sole were found on the surface sediments layer in the survey area with the maximum density of 89,240 eggs per square meter. Therefore we concluded that this area was a spawning ground of marbled sole. Eggs were found on sandy sediment at depths of 6-16 m where artificially placed stones of 1-2 m and natural stones of ca. 20-30 cm diameter were scattered. Based on the present results and other information, existence of rocks and stones is thought to be an important component to form spawning grounds and marbled sole spawns on sandy sediments adjacent to stones. The sex ratio (female/total) was significantly lower than 0.5 (P<0.01) for the specimens caught by the gill net set near the survey area during the spawning seasons. These results suggest that the migration pattern to spawning grounds was different between males and females. Key words: marbled sole, spawning ground, the Seto Inland Sea, Harima Nada