Ten, fifteen and twenty millimeter nerve defects were produced on both trunks of sciatic nerve in 18 rabbits. The stumps of the nerve were enclosed by a silicon tube in the right hind limb (slilcon group) and the left limbs were free (free group). The proximal and distal nerve stumps in both groups were elongated by using a selfdesigned nerve stretching device, and the nerve were gradually stretched by 1mm, 2mm and 3mm per day respectively. when the expected lengths were achieved, the defects of the nerve were managed by endtoend coaptation. The samples were analysed by electrophysiological examination, and light and electron microscopes. Results were as follows: (1) The nerve defect could be repaired by gradual elongation in rabbits; (2) The results of silicon group were superior to the free group; (3) The structure and microcirculation of the nerve would be damaged if the stretching speed exceeded the limit of 2mm per day. But the eventual results following repair by elongation could not reached the normal level.