The relationship of Eimeria sp. and its host fat LibyanJird (Meriones libycus) was studied on an ultrastructural level. The host cellular organelles (nucleus, mitochondria, endoplasmic reticulum and golgi apparatus) and the changes of its
infected intestinal epithelial cells during the development of parasitic stages (schizogony and gamogony) were studied and compared with those non-infected cells. The ultrastructures of intravacuolar tubules and folds in the parasitophorous
vacuole (P.V.) were described. These fine structures may involve in the transporttation of materials from the host cell to across the parasitovorous vacuole (P.V.).