Abstract: To study the damage mechanisms of coccidian infection with E. tenella, apoptosis of cecal epithelial cells from chicken with coccidiosis(E.tenella)was investigated. Chickens were infected with crude sporulated Eimeria oocysts. The pathological changes of cecal mucosa epithelial cells and enteraden epithelial cells were observed by histological section. Ultrastructural changes were monitored by transmission electron microscopy. Apoptosis was determined with TUNEL method. The results showed that at the 2nd day post infection, the number of apoptotic cecal mucosa epithelial cells was increased comparing with the control group. The most pathological changes occurred at 4-6 days post infection. Severe hemorrhage and exfoliated epithelial cells were found at the middle and posterior cecum. More seriously, cecal mucosa was entirely detached from some segment of the cecum with destroyed enteraden, degenerative or necrotic epithelial cells and erythrocytes. Other surviving cecal mucosa epithelial cells and enteraden epithelial cells showed apoptotic changes, such as cell shrinkage, chromatin condensation and aggregation at the periphery of the nucleons, nuclear fragmentation and forming apoptotic bodies. Apoptotic index showed extremely significant difference（P≤0.01） between the test and control groups. These results indicated that apoptosis of chicken′s cecal mucosa epithelial cells infected with E. tenella was more serious than the control group, specially at the epigamy phase. And the apoptosis severity is intimately related to the degree and course of coccidiosis.