The present study is the first record of a natural neogregarine infection of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) in Turkey. The infection occurs in the fat body and hemolymph of the larvae. Typical fresh navicular oocysts of the pathogen were 12.1-16.2 mu m in length and 5.9-8.5 in width (n = 50). Oocysts stained with Giemsa stain measured 11.7-14.2 mu m in length and 5.9-8.5 mu m in width. Polar plugs were recognizable using light and electron microscopy. The oocyst wall is quite thick, measuring 460 to 560 nm. Each oocyst contains 8 sporozoites. The described neogregarine has typical characteristics of members of the genus Mattesia (Family Lipotrophidaeorder Neogregarinorida) and shows similarities with Mattesia dispora in morphological and ultrastructural characteristics. The occurrence of the pathogen in different life stages of E. kuehniella was also studied. Total infection was observed as 66.98% in the investigated samples. The pathogen caused different infection levels in the larvae, pupae, and adults of the E. kuehniella, 57.06, 85, and 3.17%, respectively.