A single specimen of a juvenile Stethojulis trilineata was first collected from the coastal waters of Ulsan, Korea, in October 2012. This species is characterized by IX dorsal fin spines, 26 lateral line scales, 25 vertebrae, dark spots between the 10th and 11th dorsal fin rays, and a caudal peduncle region. The new Korean name proposed is "Se-jul-mu-ji-gae-nol-rae-gi" for S. trilineata.