A new polyclad turbellarian, Notoplana rugulosa, from intertidal rocky shore of the Sanriku coast, northeastern Japan, is described. The new species resembles N. acticola (BOONE, 1929) from California and N. japonica KATO, 1937 from the Pacific coast of central Japan in some respects, but it is well distinguished from the former by having a large bulbous seminal vesicle with a larger prostatic vesicle in the male genital organ and a larger folded Lang's vesicle in the female, and from the latter by having no penis-sheath in the male.