A gregarine parasite of the flea beetles, Phyllotreta undulata and P atra is reported and described as Gregarina phyllotretae Hoshide 1953. Gregarine infection was observed in all localities investigated during the study. Infection in the P undulata population was always higher than that in the P atra population. Maximum infections of both insects were recorded in August. Measurements of trophozoites, sporadins and syzygy forms of G. phyllotretae, new hosts, distribution, occurrence and prevalence in Turkey are reported in this paper.