After bilateral carotid artery occlusion for 30 minutes and reperfusion for 2 hours, distinct pathological changes presented in the cerebral cortex and cerebellum of rats. Compared with normal rats, nerve cell membrane fluidity significantly decreased in ischemia/reperfusion rats as detected by spin-labeling electron spin resonance, consistent with order parameter S and rotational correlation time τc measurements. Brain nerve cells from rats with ischemia/reperfusion injury were cultured with 1-100 mg/mL Buyang Huanwu decoction. Results showed that Buyang Huanwu decoction gradually increased membrane fluidity dose-dependently to normal levels, and eliminated hydroxide (OH˙) and superoxide (O2˙) free radicals dose-dependently. These findings suggest that Buyang Huanwu decoction can protect against cell membrane fluidity changes in rats with ischemia/ reperfusion injury by scavenging free radicals. After bilateral carotid artery occlusion for 30 minutes and reperfusion for 2 hours, distinct pathological changes presented presented in the cerebral cortex and cerebellum of rats. Compared with normal rats, nerve cell membrane fluidity significantly decreased in ischemia / reperfusion rats as detected by spin-labeling electron spin resonance, consistent with order parameter S and rotational correlation time τc measurements. Brain nerve cells from rats with ischemia / reperfusion injury were cultured with 1-100 mg / mL Buyang Huanwu decoction. Results showed that Buyang Huanwu decoction gradually increased membrane fluidity dose- dependently to normal levels, and eliminated hydroxide (OH˙) and superoxide (O2˙) free radicals dose-dependently. These findings suggest Buyang Huanwu decoction can protect against cell membrane fluidity changes in rats with ischemia / reperfusion injury by scavenging free radicals.