A new microsporidian parasite was discovered in Chaetocnema tibialis (Coleoptera: Chrysomelidae) in Turkey. The life cycle of the new species was examined by light and electron microscopy. It parasitizes the Malpighian tubules of C. tibialis. All development stages are in direct contact with the host cell cytoplasm and have paired nuclei (diplokaryon). Fresh spores are elongated and measure 3.82 +/- 0.3 x 1.3 +/- 0.2 mu m. The spores possess two spherical nuclei, 8-10 coils of the polar filament and a posterior vacuole. All morphological and ultrastructural features indicate that the described microsporidium belongs to the genus Nosema. The microsporidian parasite presented here differs from Nosema chaetocnemae in spore size, number of polar filament coils, tissue specificity and locality. Therefore the parasite is considered to be a new microsporidian parasite of C. tibialis. This new species has been named Nosema tokati sp. n. after the name of its host's location.