〔Abstract〕 Objective To observe the effects of TgCtwh3 and TgCtwh6,Toxoplasma gondiiof Chinese 1 dominant genotype, on the ultrastructure of hippocampal of mice. Methods Six-week-old female C57 BL/6 mice were randomly divided into three groups: control group, TgCtwh3 infection group and TgCtwh6 infection group, with 6 mice in each group. Control group was intraperitoneally injected with sterile PBS. The TgCtwh3 infected group was intraperitoneally injected with 4 000 TgCtwh3Toxoplasma gondiitachyzoites and fed for 6 days. The TgCtwh6 infected group was given 20 TgCtwh6Toxoplasma gondiicysts by gavage and fed for 6 weeks. Then, all the animals were sacrificed, the brains were obtained for preparing electron microscope specimens and observed. Results Compared with the control group, the cells in hippocampal of TgCtwh3 infected group showed nuclear shrinkage and necrosis; cytoplasmic and axon swelling; organelle disappearance; axonotmesis and other pathological changes. Compared with the control group, the cells in hippocampal of TgCtwh6 infected group showed swollen, vacuolated, crista-broken or membrane-broken mitochondria; lipofuscin deposition; dilation of golgi apparatus and other pathological changes. Conclusion Both TgCtwh3 and TgCtwh6 infected mice showed ultrastructural changes in hippocampal compared with normal mice. The TgCtwh3 group showed irreversible cell necrosis, while the TgCtwh6 group showed chronic cell damage mainly caused by mitochondrial structure destruction. These results lay a foundation to explore the pathogenesis of toxoplasmosis.