Ten species of the genus Tersilochus are found to occur in South Korea. Eight species belonging to the subgenus Tersilochus are described as new: T. fidicinus sp. n., T. gangwonus sp. n., T. iracundus sp. n., T. nigellus sp. n., T. obstinatus sp. n., T. punctator sp. n., T. serratus sp. n., and T. uncinatus sp. n. One abundant and widely distributed Palaearctic species, T. (Gonolochus) caudatus Holmgren, is recorded from South Korea for the first time. A key to 10 South Korean species of the genus Tersilochus is provided. Recently discovered finger-shaped flagellar structures are found and described in all Korean species of Tersilochus.