The fine structure of sterile cysts of Echinococcus granulosus in mice was studied by TEM. The cyst wall consists of laminated layer and germinal membrane. At ultrastructural level, the laminated layer contains microfibrillate matrix and irregularly shaped electron-dense granules. The germinal membrane comprise of tegument and cell region. Plasmalemma invagination resembling the "pinocytotic vesicle" are seen between the microtriches of the tegument, and mitochondria are seen in the basal portion of the tegument. In the cell region, there are tegumental cells, muscle cells, and glycogen-containing cells. "Nucleolar channel system" can be observed in some of the glycogen-containing cells.