The occurrence of Stenogramma interruptum in northeast Asian waters is a matter of debate. We analyzed rbcL from Korean specimens filed under the species name S. interruptum in combination with morphological observations. A partial rbcL sequence revealed that the Korean specimens were clearly distinct from other species of Stenogramma as well as S. interruptum from Europe. The morphology and anatomy of the Korean specimens were consistent with the rbcL data. Based on these results, we herein describe the new species Stenogramma guleopensis from Korea. Stenogramma guleopensis is distinguished mostly by its small size (up to 8 cm), slender thallus with narrow and parallel-sided segments, terminal branches basally constricted, two layers of cortical cells, two to three layers of medullary cells, and a gradient of two layers of smaller cells between the cortex and medulla. Further collections and careful examinations in the field will probably reveal extension of the distribution of S. guleopensis to the waters surrounding Korea.