Social parasitism was occasionally found some Polistes species as well as Vespa species like Vespa dybowskii. In this summer, we newly discovered interspecific facultative parasitic relationship between two closely Polistes species, Polistes djakonovi and Polistes mandarinus, in a rural area of Machi-ri (N35°47′35.05″ E127°15′30.48″), Wanju-gun of Jeonbuk, South Korea. Individuals of P. djakonovi closely resemble individuals of P. mandarinus in their color pattern. Accordingly, the morphological similarity between two species should motivate the parasitism for the invader species. We obviously recognized case of typical social parasitism as follows. 1) P. mandarinus dwelling together in a nest of P. djakonovi, 2) A discovered yellow cocoon cap of P. mandarinus in the nest (cf. color of cocoon cap of P. djakonovi is white). Wecollected 2 females of P. mandarinus among all 30 individuals (14 females and 16 males) in the nest. However, we could not comprehend their ecological characteristics because this phenomenon was discovered after removing of this nest.