To investigate the effects of astragalus injection on expression of brain derived neurotrophic factor (BDNF) in cerebral ischemia reperfusion injury in rats. Methods: The middle cerebral artery occlusion reperfusion (MCAO/R) rat models were established by inserting filament suture from right external-internal carotid artery and treated by intraperitoneal astragalus injection (6 mL/kg). The neurobehavioral function of rats was evaluated by Longa’s test, and neuronal apoptosis was detected by TUNEL staining with Western-blot as the quantity analysis method to detect the expressions of brain derived neurotrophic factor (BDNF). The expression of BDNF mRNA was determined by Real-Time PCR. Results: After the treatment with astragalus injection, the expression of BDNF and BDNF mRNA in rats hippocampus increased significantly compared with those of the control group. Neuronal apoptosis was significantly reduced and the animal neurobehavioral function improved significantly. Conclusion: Astragalus injection may inhibit apoptosis, promote the nerve repair, stimulate the nerve regeneration and improve the nervous behavioral function by up-regulated the expressions of BDNF.