Abstract： Objective To study effects of hyperbaric oxygen (HBO) on apoptosis of nerve cells following focal cerebral isehemia reperfusion in rats. Methods The rat middle cerebral artery occlusion reperfusion (MCAO) model was developed by using the intraluminal filament method. 32 rats were randomly divided into2 groups: the control group (n=16) and the HBO group (n=16). Then, the 2 groups, each consisting of 4 animals, were further subdivided into 4 groups, i.e. the hour 12 reperfusion group, the hour 24 reperfusion group, the day 3 reperfusion group and the day 5 repcrfusion group. Following 1-hour cerebral ischemia, the experimental animals were exposed to HBO. Then, the expression of apoptosis was determined with HE staining and cell apoptosis detection. Pathological changes in neural cells and distribution of apoptosis were observed in the study. Results In the control group, the apoptosis of neural cells could be detected 12 hours after reperfusion following cerebral ischemia, the number of apoptosis cells gradually increased with the extension of time, reached a maximum at hour 24, then subsided gradually. In the HBO group, the number of cells was significantly lower than those in the control group at the same time point. Conclusions HBO could inhibit the apoptosis of neurons, protect neural cells and help to enhance recovery of neural functions following cerebral ischemia.