A new species of the family Cyatholaimidae Filipjev, 1918 was collected from Gwangyang Bay, Korea. The new species belongs to the genus Marylynnia Hopper, 1977 on the basis of the following morphological characters: 1) two types of cuticular pores, 2) dorsal tooth with a pair of small subventral teeth, 3) cup shaped precloacal supplements, and 4) conico-cylindrical tail. Marylynnia denticulata n. sp. is closely related to Marylynnia malsa (Hopper, 1972) by virtue of body length, the number of cervical setae, spicule length, the presence of denticles lining the distal portion of the gubernaculum, and gubernaculum length. However, the new species differs from M. malsa by the location of the cervical setae, the shape of the spicule and gubernaculum, and the number of precloacal supplements. This is the first description of the family in the study area.