It was first recorded that Elasmus japonicus Ashmead had occurred from three Polistes nests in Busan city, Wanju-gun, and Pyeongchang-gun of South Korea. The 2 females and 14 males were collected from the nest of Polistes rothneyi koreanus in Busan city (N35°17′57.71″ E129°06′33.24″), 12 females and 2 males from P. djakonovi in Wanju-gun (N35°47′35.05″ E127°15′30.48″), 18 females and 3 males from P. snelleni in Pyeongchang-gun (N37°39′7.84″ E128°35′15.81″). P. rothneyi koreanus and P. djakonovi were first recorded as new hosts. To date, two Elasmus species, E. nephantidis and E. viridiceps, have been reported from South Korea. In this study, we provide diagnosis, description, and photos of female and photos of male of E. japonicus.