Summary The length–weight relationships (LWRs) of three endangered tidal pool fishes, Spratelloides gracilis (Temminck & Schlegel, 1846), Atherion elymus Jordan & Starks, 1901, and Enneapterygius etheostomus (Jordan & Snyder, 1902), from Jeju Island, Korea, were analysed. A total of 280 specimens were sampled using hand nets (mesh size 1 mm) or by dredge (mesh size 5 mm) from July 2015 to July 2016. This study provides the first LWRs for two species, a new LWR for one species, and a new maximum length data for two species.