The objective was to observe the effect of electroacupuncture on nitric oxide synthase (NOS) expression in the spinal ganglia and spinal cord. Methods: The nicotinamide adenosine dinucleotide phosphate diaphorase (NADPH-d) method was used after electroacupuncturing "Zusanli" (ST 36) point. Results: The numbers of heavily staining NOS positive neurons in the spinal ganglia and spinal cord were increased markedly on the acupuncture side as compared with the non-acupuncture side and control groups. The heavily staining NOS positive fibers and terminals were also increased markedly in the lamina I of spinal cord on acupuncture side. Conclusion: The NOS expression was significantly enhanced by electroacupuncture in the spinal ganglia and spinal cord. So it is possible that NO is one of the important morphological foundations for acupuncture effects.