Cadmuim poisoning had been described to result in the disturbance of the olfactory function, but the mechanism has not been disclosed. This study was designed to observe morphological changes of the olfactory epithelium of the nasal septum and cribriform plate induced by cadmuim poisoning in rats. The rats were injected subcutaneously with 0.1% solution of cadmium chloride in a dose of 1.7mg/kg everyday for 3 weeks. The rat of the control group were injected with the same volume of saline. The control and experimental animals were sacrified at 8 hours following the last injection. The olfactory epithelium of the nasal septum and cribriform plate was taken, and investigated by scanning and transmission electron microscope. The results were as follows : 1) The olfactory ciliary mat was lost and the olfactory vesicles were atrophied. 2) The olfactory cells in the olfactory epithelium were injured seriously. There were many vacuoles and electron-dense bodies in the cytoplasm and olfactory vesicles. Mitochondria were also degenerated and rough endoplasmic reticulums were dilated and lost some of ribosomes. Olfactory dendrites were also degenerated and contained several vacuoles. 3) The supporting cells in the olfactory epithelium were also injured. They contained many electron-dense bodies and vacuoles in their cytoplasms. These findings suggest that cadmium poisoning can result in pathologic degenerative changes of the olfactory cell bodies, olfactory dendrites and supporting cells in the olfactory epithelium.