Philodromidae Thorell, 1869 is one of the most diversified and largest families comprising 522 species in 29 genera within the order Araneae Clerck, 1757. The genus Thanatus C. L. Koch, 1837 comprise 99 species of the family and four species of the genus Thanatus (Philodromidae) have been recorded in Korea: T. coreanus Paik, 1979, T. miniaceus Simon, 1880, T. nipponicus Yaginuma, 1969, and T. vulgaris Simon, 1870. Two females of T. arcticus Thorell, 1872 were collected by sweep net between the shrubs in mountainous mixed forests from Mt. Chiaksan National Park, Wonju-si, Gangwon-do and Mt. Naejangsan National Park, Jangseong-gun, Jeollanam-do. The present study describes T. arcticus with measurements and taxonomic illustrations.