Objective To observe expression of neuronal nitric oxide synthase (nNOS) and inducible NOS (iNOS) in nerve and dominated muscle of rat after injury of sciatic nerve.Methods 12 female SD rats were divided into 4 groups, right sciatic nerve was squeezed by using forceps for 0.5hr, 1hr, 2hr and 5hr respectively. Then right sciatic nerve and gastrocnemius was isolated and RNA was extracted by using Trizol reagent and meanwhile, the left sciatic nerve and gastrocnemius was used as a normal control. NOS expression was detected by using RT PCR and RNAase protection assay (RPA), and GAPDH was used as an internal standard. The density of PCR and RPA bands was determined by using NIH image software.Results 2 NOSs did not vary in nerve tissue in 4 groups, but in muscle, nNOS increased in 1h group, decreased in 2h group and increased in 5h group; iNOS decreased in 1h and 2h groups but increased in 5h group when compared to normal control.Conclusion Injuring of nerve does not effect NOS expression itself within short period, but effects the dominated muscle via the transmission of non NOS nerve signal.