Prior to this study, only 8 species of oak gall-forming wasps were known from Korea. After material examination and an exhaustive bibliographic revision, a total of 17 oak gall wasps species have been reported. The following species correspond to new records: Andricus hakonensis (Ahmead); A. pseudocurvator Tang & Melika; A. songshui Tang & Melika; Cerroneuroterus folimargo (Monzen); C. monzeni (Dettmer); C. vonkuenburgi (Dettmer); Neuroterus hakonensis Ashmead, Trichagalma acutissimae (Monzen), T. formosana Melika & Tang. It was impossible to obtain adult specimens for all the species, and and the following species are recorded only based on galls: Andricus kashiwaphilus Abe; A. mukaigawae (Mukaigawa); A. pseudoflos (Monzen); A. targionii Kieffer; Cerroneuroterus folimargo (Monzen); C. monzeni (Dettmer); Neuroterus hakonensis Ashmead; Trichagalma acutissimae (Monzen). The species Dryocosmus kunugiphagus Ide & Abe, 2015 is transferred to the genus Plagiotrochus: Plagiotrochus kunugiphagus (Ide & Abe, 2015) n. comb. Additionally a new subspecies of Trichagalma formosana is described to include the material from Korea and Mainland China, closely related but morphologically different to the Taiwan populations. For each species live cycle, morphology of galls, hosts, phenology, and distribution are commented. In some of them taxonomic or morphological comments are mentioned and a key of agamic Trichagalma with dark smoky pigmented spots in the forewing is added. All galls are illustrated. An up-to-date checklist of the Korean Cynipini is provided. The previously reported species from Korea (Andricus noliquercicola Shinji, 1938; Aphelonyx crispulae Mukaigawae, 1920; Neuroterus narae Shinji, 1941 and Neuroterus nawai Ashmead, 1904) are here excluded from the Korean species list.