Objective:To investigate the mechanism of iNOS in ischemia－reperfusion injury of rat spinal cord. Methods:Forty－two Sprague－Dawley rats were randomly divided into three different groups: Sham－operated group (n = 6),ischemia－reperfusion group (I/R,n = 18),and iNOS inhibitor group(I/R + AG,n = 18). In sham－operated group,peritoneotomy was performed without abdominal aortic cross－clamping (AACC),however,rats in I/R group and iNOS inhibitor group experienced 1 h AACC followed by 6 h,12 h,24 h reperfusion, respectively. After operation,rats in sham－operated and I/R group received an intraperitoneal injection of the carrier solutions (5 ml/kg of 5% DMSO),while rats in iNOS inhibitor groups received the treatment of AG at the dose of 150 mg/kg (i.p.). We examined the neurological motor function using ‘Tarlov’s score’ at 6 h,12 h and 24 h,alterations of spinal cord neurons morphologically by transmission electron microscopy (TEM). Immunofluerescent staining with anti－NeuN,a specific marker for neurons,was performed to observe the number of surviving neurons in different conditions. The level of iNOS,BAD,p－BAD,14-3-3, and cytochrome C were detected by Western blot;the interaction of BAD and 14-3-3 was determined by coimmunoprecipitation analysis. Results:①The motor functions of the hind limbs of the sham－operated rats were normal. Rats in ischemia－reperfusion group were observed with significant reduce on hind limb movements (P < 0.05) in every reperfusion time compared to those in inhibitor group. ②The number of NeuN－positive cells (surviving neurons) in I/R group and iNOS inhibitor group was less than that in sham－operated group,while the number in iNOS inhibitor group was more than that in I/R group (P < 0.05). ③In the sham－operated group,no apoptotic neuron was noted. In ischemia－reperfusion group and iNOS inhibitor group,numerous apoptotic neurons could be detected. However the severity of apoptotic neuron in inhibitor group was less than that in I/R group. ④In the sham－operated group,iNOS was hardly detected at an extremely low level and was increased in a time－dependent manner in I/R group and iNOS inhibitor group,but the expression of iNOS in iNOS inhibitor group was lower than that in I/R group at each reperfusion time (6 h,12 h,24 h) (P < 0.05). Simultaneously,the change of cytochrome C was the same as the iNOS expression mode. In addition,the expression of p－BAD started to decrease at 6 h and decrease remarkably at 12 h,24 h in I/R group and iNOS inhibitor group,but the extent of decrease of p－BAD expression in iNOS inhibitor group was lower than that in I/R group (P < 0.05). ⑤In I/R group,the level of p－BAD/14-3-3 dimerization began to decrease since the reperfusion process started. However in the iNOS inhibitor group,the trend was alleviated by AG treatment (P < 0.05). Conclusion:iNOS inducing apoptosis of neurons in spinal cord ischemia－reperfusion injury is involved in dephosphorylating BAD, and it can lessen spinal neurons apoptosis by inhibiting the activity of iNOS.