Objective To clarify the pathologic change of the motor neuron on spinal cord ischemia reperfusion injury delayed paraplegia. Methods The infrarenal aorta of White New Zealand rabbits (n=24) was occluded for 26 minutes using two bulldog clamps. Rabbits were killed after 8, 24, 72, or 168 hours (n=6 per group), respectively. The clamps was placed but never clamped in sham-operated rabbits (n=24). The lumbar segment of the spinal cord (L5 to L7) was used for morphological studies, including hematoxylin and eosin staining, the expression of bcl-2 and bax proteins in spinal cord was detected with immunohistochemistry. The apoptotic neurons in spinal cord were measured with terminal deoxynucleotidyl transferase mediated dUTP-biotin nick end-labeling of DNA fragments (TUNEL) staining. Results Delayed paraplegia occurred in all rabbits of ischemia reperfusion group at 16-24 hours, but not in sham groups. Motor neurons were selectively lost at 7 days after transient ischemia. After ischemia, the positive expression of bcl-2 protein were in the sham controls but decreased significantly as compared with that of the IR group (P＜0.01), especially in 72 hours reperfusion. The positive expression of bax protein were also in the sham controls, but increased in the IR group, especially in 72 hours reperfusion; In addition, TUNEL study demonstrated that no cells were positively labeled until 24 hours after ischemia, but nuclei of some motor neurons were positively labeled at peak after ischemia reperfusion at 72 hours. Conclusion Spinal cord ischemia in rabbits induces morphological and biochemical changes suggestive of apoptosis. These data raise the possibility that apoptosis contributes to neuronal cell death after spinal cord ischemia reperfusion.