A new species of cotylean flatworm, Acerotisa ochotensis sp. n., is described. Worms were found at depths from 2.5 to 88 m in several localities in the western Sea of Okhotsk (Tugursky Bay, northern extremity of Sakhalin Island, and Bolshoi Shantar and Iona islands). The new species can be distinguished from other members of the genus Acerotisa by the set of features: the complex male copulatory organs located under the front part of the pharyngeal cavity, close arrangement of male genital and mouth openings, a relatively large number of eyes in the cerebral and marginal eyespots, the presence of anastomoses between intestinal branches, and the cylindrical shape of the pharynx.