Orussidae is a unique family belonging to the ‘Symphyta’, Hymenoptera. It is a small group of parasitoid sawflies, consisting of about 90 known extant species in 15 genera in the world. Most species of Orussidae are thermophilous and imagines are active during the hottest hours of the day. Therefore, orussids are rarely collected. They are known to be idiobiont ectoparasitoids of larvae of wood-boring beetles such as Buprestidae and Cerambycidae or Hymenoptera such as Siricidae and Xiphydriidae, although records of orussids parasitizing introduced siricids in New Zealand do not constitute a natural host relationship. Within the family, Orussus is the largest and most widely distributed genus. Currently, 28 valid species are recognized. Recently, Vilhelmsen et al. (2014) reported three new species of the genus Orussus from the Oriental region. Here we describe a new species, Orussus sp. nov., from South Korea and provide a revised key to the eastern Palaearctic species of Orussidae. Also, phylogenetic analyses place the new species basally in Orussus, together with other species from the Far East.