To assess the influence of diabetes mellitus on the healing of segmental defect of rat, a defect measuring 5mm was made at right sciatic nerve in thirty-three adult female Wistar rats(control group:17, diabetic group:16). To induce diabetes in rats, Streptozotocin(50mg/kg body weight) was injected into tail vein after dissolution in saline solution. Both proximal and distal nerve ends were connected with 9mm long silicone tube, and the tube was filled with 10µl collagen(Vitrogen 100) solution. Two and 4 weeks after the operation, electromyographic study(latency period and amplitude) and histologic examination(the number of myelinated axon, non-neuronal cell, and vessel at mid-chamber level, the mid-chamber cross-sectional area) after toluidine blue staining were carried out. From the results, we concluded that diabetes mellitus retarded the healing process of segmental defect of sciatic nerve in rat. And we might suggest that if we meet this situation in clinical practice, we have to consider some supportive measures to overcome the bad effect of diabetes mellitus on the healing of nerve defect.