Within the genus Macrosiagon Hentz, 1830, M. nasuta (Thunburg, 1784) (Coleoptera: Ripiphoridae) is one of the most thoroughly investigated parasitoids with respect to its host requirements. We report a new host record of M. nasuta, Eumenes labiatus labiatus (Hymenoptera: Vespidae) from Taiwan based on a specimen reared from a E. l. labiatus nest. This observation, along with the published data, support the notion that M. nasuta is exclusively a parasitoid of vespid wasps in the subfamily Eumeninae.