Ecklonia cava ssp. kurome is the only perennial kelp which is distributed in the central and western areas of the Seto Inland Sea, and is an important component of macroalgal beds in these areas. Biomass and production rates of this species were surveyed at three islands (Heigun-jima Is., Kata-shima Is. and Yashiro-jima Is.) in the western Seto Inland Sea during 2012–13. The mean biomass of dominant stands in the luxuriant season (June–July) ranged from 0.7 to 1.3 kg DW m-2 and the mean adult thallus density was approximately in the range of 10–20 inds. m-2. Net production was estimated by the leaf-marking method at Kata-shima Is. and Matsu-ga-hana in Yashiro-jima Is. Estimated production rates were 10.4–15.6 g DW m-2 d-1 in the luxuriant season, 1.8–5.3 g DW m-2 d-1 in the senescent season (October–November), and 5.8–12.9 g DW m-2 d-1 in the growth season (February–March). These trends were similar to those for E. cava ssp. kurome and its closely related E. cava ssp. cava reported in the Pacific Ocean and East China Sea, respectively. Morphological characteristics, such as stipe length, length/width ratio of the central blade and the primary pinna number index (PPNI) of adult E. cava ssp. kurome thalli exhibited significant differences in the luxuriant season among the survey sites, which reflected variable environmental conditions in their habitats.