A new species, Attheyella namkungi sp. nov., is described from Gosu cave at Danyang, Chungcheongbuk-do, South Korea. This species bears a superficial resemblance to A. coreana Miura, 1969 in having a 2-segmented mandibular palp with only four smooth apical setae, and in the armature formulae of the antennary exopod and thoracic legs. However the new species is clearly distinguishable by the non-sexually dimorphic caudal rami, two long plumose setae and a short seta on leg 6, and the absence of the setular row at the inner lateral margin of each caudal ramus. The new species is characterized from other congeners by having two adjacent inner spines on female leg 3 endopod-2, the caudal ramus twice as long as its width, absence of a barbed apophysis on male leg 3 endopod-2, and the seta number of legs 5 and 6. A key to the Korean species of the genus Attheyella is provided.