When.direct approximation of the ends of the injured nerves is impossible, nerve autografting is widely used in these days. Authors tried to observe nerve regeneration in time sequence of nerve autografting and tried to find out the most optimal time for nerve autografting in experimental study. The Sprague-Dawley mice were used in performing nerve autografting and it performed with the segment of the opposite sciatic nerve as a donor nerve after resection of a sciatic nerve. The results obtained were as follows: 1. The regeneration of axon can be observed well in the first observation of 2 weeks after nerve autografting within 2 days, but active myelination can be observed apparently 4 weeks after grafting. 2. The groups of grafting within 2 days after nerve resection showed more rapid nerve regeneration and less atrophy of the reinnervated skeletal muscle than the groups of grafting over 1 week after nerve resection did. 3. In case which has been grafted at 4 weeks after nerve resection, there was abundant axonal proliferation at 4 weeks after grafting. 4. Changes of the reinnervated skeletal muscle in the groups of grafting within 2 days were subtle, but the groups of grafting after 1 week showed irregular neurogenic atrophy although nerve regeneration has been active at 8 weeks after grafting. 5. Although the functional effect can not be evaluated exactly, the result of autograft showed relatively good evidence of nerve regeneration even after grafting has been performed 16 weeks after the nerve injury.