This report is the first description of a pathogen or parasite in the predator beetle Rhizophagus grandis (Coleoptera, Rhizophagidae) and the first report of a naturally infected beetle from the family Rhizophagidae (Coleoptera). The hemolymph of the beetle was infected by the parasitic green alga Helicosporidium. The typical cysts of Helicosporidium contain three ovoid cells and one helical, filamentous cell. The morphological characteristics are revealed by light and electron microscopy. In total, 6.8% of the beetles were infected by the parasite. The infection was observed at two of five Turkish laboratories which rear Rhizophagus grandis. The infection was 23.6'/,) at the laboratories in Artvin and 9.8% in Ordu. (c) 2007 Elsevier Inc. All rights reserved.