Objective To investigate the effects of transplanted olfactory ensheathing cells (OECs)and L-NNA on neuronal survival and axon regeneration in Clarke’s nucleus (CN) after spinal cord hemisection of rats. Methods Twenty rats were divided into control group, L-NNA group, OECs group, and OECs+ L-NNA group after spinal cord hemisection. OECs were transplanted into the injured site of spinal cord and L-NNA was injected in OECs+L-NNA group of rats. Thirty days after operation, NADPH enzyme histochemistry, immunohistochemistry, neutral red staining, HE staining and fluorogold retrogradatic labeling were applied to determine the survival and axon regeneration of neurons at L1 CN in 4 groups of rats. Results 1. The number of neuronal survivals at L1 CN in OECs group and L-NNA group was higher than that in control group. The effect of promoting the survival of big, middle and small neurons at CN of spinal cord in OECs group and L-NNA group was shown by differential counts. The effect of promoting neuronal survival was the most significant in OECs+L-NNA group. 2. The regenerated axons were observed at the injured site of spinal cord and the neuron bodies labeled by fluorogold retrogradation were found at L1 CN in OECs group and OECs+L-NNA group. 3. Compared with those in control group, nitric oxide synthase (NOS) positive neurons were increased in OECs group, decreased in L-NNA group, and were no difference in OECs+L-NNA group.Conclusion Transplanted OECs or L-NNA may facilitate the survival of injured CN neurons of spinal cord. The combination of transplanted OECs and L-NNA can preferably promote the survival and axon regeneration of injured CN neurons