A new taxon, Hymenophyllum wrightii f. serratum C.S. Lee & K. Lee (Hymenophyllaceae), forma nov. was collected and described from forests in Mt. Halla, Jeju-do, Korea. This taxon, H. wrightii f. serratum C.S. Lee & K. Lee (vernacular name: ‘Gu-reum-cheo-nyeo-i-kki’) was distinguished from H. wrightii f. wrightii by having smaller leaves, broader basal part of leaf blade, broad-ovate laminae, larger sori and serrate margins of lips of involucres. The new taxon’s name is based on serrate margin shape of the lips. A Korean name, ‘Gu-reum-cheo-nyeo-i-kki’, was newly given based on its habitat. Descriptions and its photograph in the habitat are provided along with a key to the species of Hymenophyllum from Korea.