Abstract： Objective To study effect of hyperbaric oxygen (HBO) on astrocytes in adult rats with cerebral ischemia-reperfusion injury. Methods Sixty-four adult SD rats were used for the experiment. Middle cerebral artery occlusion (MCAO) model was developed with thread occlusion, which was followed by reperfusion 1.5 hours later and assessment of neural function. Those animals with modeling failure were rejected for the experiment. Other rats were divided randomly into the ischemia-reperfusion (IR) group and the HBO treatment group, each consisting of 32 rats. Rats in the HBO treatment group received 60 minutes of HBO treatment, 4 hours after ischemia-reperfusion, one session a day, with the therapeutic pressure of 0. 28 MPa. Following development of the model, the animals in the 2 groups were sacrificed on the 4th, 8th, 11th, and 31st days respectively, and cerebrums were collected for paraffin sections. Glial fibrillary acidic protein (GFAP) in corpus striatum was detected with immunohistochemical staining, and observed with light microscopy. In the meantime, integrate optical density (IOD) of GFAP was measured and related analyses were made. Results For the same group, at the same time points, the IOD of GFAP in the ischemic penumbral regions of the IR group or the HBO group was significantly higher than that in the opposite hemisphere( P ＜0. 05), and no statistical differences could be seen in the IOD of the opposite hemisphere at the same time points ( P ＜ 0. 05 ). No statistical significance was shown in the IOD of GFAP for the IR group on the 3rd, 7th, and 10th days ( P ＞ 0. 05 ), nevertheless, IOD level on the 30th day was obviously higher than those of other time points(P ＜ 0. 05 ). For the HBO group, no statistical significance could be noted in the IOD of GFAP, when comparisons were made between the 3rd and the 7th days, and also between the 7th and the 10th days ( P ＞0. 05 ). The IOD of GFAP in penumbral regions on the 10th day was significantly higher than that of the 3rd day ( P ＜ 0. 05 ), and with statistical significance, when comparisons were made between the 30th day and the other time points (P ＜ O. 05 ). Moreover, IOD levels at various time points were all significantly higher than those of the IR group (P ＜ 0. 05 ). Conclusions The expression of GFAP could be regulated by HBO at different time points, in other words, HBO treatment might have greta significance on the recovery of the neural function in case of ischemic brain injury.