Effective pollinators of Arisaema nambae Kitam., endemic to western Okayama and eastern Hiroshimaprefectures, western Japan, were determined, and 113 insects from 24 spathes of A. nambae in threepopulations in Okayama Prefecture were collected. Most floral visitors were fungus gnats (Mycetophi lidae and Sciaridae). Their maximum body width was less than the internal diameter (ca. 2 mm) of theexit at the bottom of the staminate spathe. Pollen grains of Arisaema attached to the bodies of fungusgnats collected from pistillate spathes provided evidence that they visited the pistillate spathe afterescaping from staminate spathes. Based on their visitation frequency, size compatibility between theirbody and the exit from the staminate spathes and the pollen loads they carry, fungus gnats appear to playan important role in the pollination of A. nambae.