A marine algal species was collected from Sacheonjin, Gangneung located on the eastern coast of Korea during a survey of marine algal flora. This alga shares the generic features of Membranoptera belonging to the subfamily Delesserioideae and is characterized by the presence of combined features of membranous, monostromatic thalli attached by a solid discoid holdfast, blades with a conspicuous terete stipe-like midrib and microscopic lateral veins, entire margins, irregularly alternate to dichotomous branching, and obtuse apices growing apically. In a phylogenetic tree based on rbcL sequences, the Korean alga nests in the same clade with M. alata from the eastern North Atlantic. The genetic distance between both the sequences within the clade was calculated as 0.0%. Based on the morphological and molecular analyses, this Korean species is identified as the generic type, M. alata. This is the first record in the list of Korean marine algal flora.