Objective To evaluate the effects of cerebral ischemia/reperfusion or/and icariin on expression of cytochrome C oxidase subunitⅡ(COⅡ) mRNA in mice. Methods The mouse model of transient cerebral ischemia/reperfusion was made by bilateral occlusion of common carotid arteries and ischemic hypotension/reperfusion. The mice were divided into several groups at random: normal control group, model group and icariin preventive treatment group (100 mg/kg). The changes in expression levels of COⅡ mRNA in mice cerebral tissue were detected by RT-PCR at different time points. Results The levels of CO Ⅱ mRNA in model group had no significant changes at 1 h and 24 h after cerebral ischemia/reperfusion as compared with that in control group, but decreased remarkably at 3 h (P