Abstract: Objective: To explore the effects of nitric oxide on the mechanism of diabetic neuropathy. Methods: The changes of nitric oxide synthase （NOS） expression in the brain of diabetic rats were measured by the histochemiscal technique with nicotinamide adenine dinucleotide phosphate （NADPH-d）. Results: After inducing the model of diabetes for three months, the positive neurons of NOS in the brain contex were obviously decreased in the diabetes group than the normal control group. While the positive neuron of NOS were found in the hippocampal area of diabetes group. Conclusion: The changes of NOS expression may be a factor in the impact of diabetes on the central nervous system.