Larval stages of Callipogon relictus (Semenov) (Coleoptera: Cerambycidae), a gigantic longhorn beetle designated as a natural monument of Korea, has never been studied as it is hardly discovered in nature. The DNA barcoding gene, mt-COI, was used to identify a dead larva found in the Gwangneung forest of the Korea National Arboretum. Based on the result, we provide the morphology of the immature stage, with the illustrations of diagnostic characteristics.