Mice inhaled ethylene oxide at concentration of 360 mg/m3 for two hours a day, six days a week for 14 weeks. At the end of second and third month, the neurons located at anterior horn of lumbar spinal cord were observed under transmission electron microscope and scanning electron microscope with freeze etching. The results showed that the morphological changes in neuron cells became more obvious as the inhalation period prolonged. Following changes were observed : The distribution of integrating proteins in neuron membrane changed from normal stochastic into clustered one, the endoplasmic reticulum reduced in number and appeared as small vesicles, the ribosomes attached to the surface of rough endoplasmic reticulum were also decreased in number, arranged irregularly, disintegrated or even degranulated. The numher of mitochondria was also decreased. Observed aiso were the swelling of the axons of myelinated nerve fibers and loss of stratification of their myelin sheaths. The above results indicated that the ethylene oxide can induce structural changes in neuron cells, and this inevitably may cause functional abnormality of nervous system and manifestation of neurotoxic symptoms in ethylene oxide exposed individuals.