Scolecenchelys borealis was first added to the Korean fish fauna based on one leptocephalus specimen (total length (TL) 59.2 mm) collected from Dokdo, in the East Sea. Recently, however, Scolecenchelys borealis has been treated as a junior synonym of Scolecenchelys aoki, necessitating review of the scientific name S. borealis. This study describes the morphological characteristics of S. aoki based on an adult specimen (TL 230.0 mm) collected from the sea south of Korea and compares its mitochondrial DNA 12S rRNA sequence with that of the S. borealis leptocephalus. The adult S. aoki is characterized by several morphological features: vertebral formula 59-55-135; preanal lateral pores 55; infraorbital pores two; teeth on upper jaw visible externally when the mouth is closed; the dorsal fin originates just behind the anus; both jaws and vomerine teeth are conical, arranged in two rows. An analysis of an 886-base paire sequence of the 12S rRNA showed that adult S. aoki was concordant with the S. borealis leptocephalus (sensu Ji et al., 2012), indicating that both are the same species.