This study was conducted to examine the pathological changes of rat peripheral nervous system during exposure to tellurium known to be a demyelinating agent by using teasing nerve fiber method and quantitative light microscopic analysis by image analyzer. The pellet containing 1.2% of tellurium were fed for 3, 5, 7, 9, 13 days to male wistar rats (21 days old) and then neurologic symptom and the feature of nerve fiber myelination were studied. From this study, following results were obtained. In 3 days treated group, it showed various neurologic symptom and teased nerve fiber showed slight irregularity of the myeline sheath. In 5 days and 7 days treated groups, it showed the segmental demyetination in larger size fiber and widening of nodes of ranvier. In 9 days and 13 days treated groups, the remyelinated fibers were observed and it was generally small in size. We consequently suggest that teasing nerve fiber method and quantitative analysis of nerve fiber were useful pathologic screening method of neurotoxicity of the peripheral nervous system.