An aeolid nudibranch species Flabellina athadona (Bergh, 1875) is newly recorded from Korean waters. This species is distinguished from other congeneric species by the following characteristics: translucent white body, deep orange colored digestive glands, plenty of white specks, and a reversed Y-shaped marking on the head between rhinophores and oral tentacles. In this report, we also provide an identification key for the genus Flabellina in Korea, photographs, and diagnostic characteristics of F. athadona. Molecular identification using mtDNA cox1 partial sequences is also provided to help differentiate F. athadona from some of its closely related congeneric species.