Abstract： Objective To study the effects of HBO at different pressures on apoptosis following spinal cord injury in rats and also to investigate ideal pressure value of hyperbaric oxygen(HBO) on spinal cord injury (SCI). Methods The SCI model was established with Allen's weight dropping by using 90 SD rats. Then, the animals were randomly divided into 5 groups following SCI: the control group ( group A); the HBO treatment group at 0. 15 Mpa (group B); the HBO treatment group at 0. 20MPa (group C); the HBO treatment group at 0. 22 Mpa ( group D); the HBO treatment group at 0.25 Mpa ( group E). Segments of injured spinal cord were collected from the animals of the 5 groups for studies on the 3rd, 7th, and 14th days after injury. The apoptosis cells were labeled with Tunel and the neurologic function of the spinal cord was assessed in the open field ( the BBB score ). Results The number of Tunel - positive cells decreased considerably and the BBB score improved significantly in all the animals of the HBO groups when compared with those of group A ( P ＜ 0. 05 ). Same results were found when the group C, group D and group E were compared with group B, with statistical significance( P ＜0. 05). The number of Tunel-positive cells were decreased considerably and the BBB score improved significantly on 3rd and 7th days in group E, when compared with those of group C( P ＜ 0. 05 ), with statistical significance( P ＜ 0. 05 ). However, no statistical significance could be noted on the 14th day (P ＜0.05). Conclusions HBO could inhibit apoptosis in rats following spinal cord injury, which might be correlated with the increase of pressure within a certain range.