AbstractMitochondrial DNA (mtDNA) sequences, which serve as DNA barcodes, have been used to associate immature and adult stages of insects and to delineate species. The partial mitochondrial cytochromecoxidase subunit I (COI) gene sequences for South Korean Megaloptera (all known in the adult stage) were tested to identify undetermined larvae as a rapid and effective method from 31 specimens (16 adults and 15 larvae). The COI gene sequences distinguished all six known Megaloptera species, with a low genetic distance between larvae and adults (0.50±0.21%). Based on the COI gene sequences, we associated five types of larvae with known adults including the following four species of newly described larval stages:Sialis annaeVshivkova, 1979 (Megaloptera: Sialidae);Neochauliodes formosanus(Okamoto, 1910) (Megaloptera: Corydalidae);Parachauliodes asahinaiLiuet al., 2008 (Megaloptera: Corydalidae); andProtohermes xanthodesNavás, 1913 (Megaloptera: Corydalidae). The known larval stage ofSialis koreanaJung and Bae, 2012 (Megaloptera: Sialidae) was confirmed, and the morphological variation in the male genitalia ofSialis longidensKlingstedt, 1932 (Megaloptera: Sialidae) is discussed. A larval key to the six South Korean species of Megaloptera is provided.