Abstract: A single Eirneria sp, oocyst isolated from mouse feces was inoculated into each mouse orally,and the mice were infected. Through observing the morphology,time for spora-tion, prepatent period, and parasitic sites etc. of the oocysts, they were identified as oocysts of E. ferrisi. The pathogenicity and the regularity of the oocysts shedding were also studied.

Key words: E. ferrisi, Oocyst, Biologic property, Mouse