Abstract: The cysts by SEM were ovoid shaped, approximately 9-10×6-7μm. The surface of cyst wall was rough instead of smooth. The cyst wall viewed with the freeze-etching technique was composed of many laminar layers of membrane. They were parallel to each other and numbered 10 or more.The thickness of cyst wall by TEM was 0.16-0.29μm. A space was seen between the parasite and the cyst wall, in which flagellar structures were cross sectioned. There were many vacuoles underlying the dorsal cell membrane of the parasite. But neither mitochondria nor endoplasmic reticulum and Golgi apparatus could be found except two different sizes of granules. Section through the regions of the nucleus shows two nuclei. The basal bodies were located near the midline line between the anterior poles of the nuclei, emerging anterior, posterior-lateral and caudal flagella. Parallel rows of micro-tubules with perpendicular ribbon-like structures were randomly distributed in the cyto-plasm.