A newly recorded hyalid species, Protohyale (Boreohyale) triangulata (Hiwatari, 2003), of Korean waters is reported with a description and illustrations. In this paper, the validity of its generic and subgeneric categories is considered. Protohyale triangulata has a specific shape of the propodus of gnathopod 1 in the matured male, forming a triangle with a subquadrate posteroproximal corner, and the palm and the posterior margin are not clear. This major characteristic feature serves to distinguish it from other Korean hyalid species. We also reexamined some previous reports of Korean hyalid species. It seems that this species had been confused with Hyale rubra in Korea.