Objective：To investigate the effects of immunosuppression treatment on peripheral nerve injury and regeneration in rats. Methods; Forty-nine SD rats were randomly divided into 7 groups： sciatic nerve （in the middle of left thigh） forcepscrushing＋ cyclophosphane, transecting ＋ cyclophosphane, resecting groups ＋ cyclophosphane, forceps-crushing ＋ normal saline, transecting＋ normal saline, resecting groups＋ normal saline, and blank control groups. Cyclophosphane and normal saline were intraperitoneally injected into rats post-operatively. Peripheral nerve regeneration and its related function were assessed by walking track analysis,electrophysiology and histomorphology; immunohistochemistry method was used to evaluate the local autoim- mune reactions 12 weeks after operation. Results： Cyclophosphane treated animals had higher scores of sciatic function index （SFI） compared to animals in the corresponding normal saline groups. The electrophysiological （nerve conduction velocity） and morphological examinations showed better regeneration of the myelinated axons in immunosuppression treated animals compared to the corresponding normal saline groups. The immunohistochemistry showed that the intensities of the local immunological response in immunosuppression groups were obviously lower as compared to the corresponding normal saline groups. Conclusion： There is local autoimmune reaction in post traumatic nerve regeneration and this autoimmune reaction may influence nerve regeneration. Cyclophosphane treatment can suppress this autoimmune reaction and improve the micro-environment for nerve regeneration