We investigated nerve regeneration following the repair of a segmental nerve defect induced by direct end-to-end neurorrhaphy after simultaneous gradual lengthening of both proximal and distal nerve stumps in rats. A 15-mm-long nerve segment was resected from the sciatic nerve of each rat. The proximal and distal nerve stumps, respectively, were directly lengthened at a rate of 1 mm/day using a custom-made external nerve-lengthening device. After being lengthened for 14 days, both nerve stumps were refreshed, and direct end-to-end neurorrhaphy was performed. For a control, 15-mm nerve grafting was performed immediately after nerve resection. Nerve regeneration was evaluated by motor nerve conduction velocity, muscle contraction force, and histological studies at 6, 8, and 14 weeks after initial nerve resection in both groups. As a result, at 8 and 14 weeks, the motor nerve conduction velocity was significantly higher in the nerve-lengthening group than in the autografting group. In addition, at 14 weeks, the tetanic force and wet weight of the gastrocnemius muscle were significantly higher in the nerve-lengthening group than in the autografting group. Histologically, the mean axonal diameter of myelinated nerve fibers and the total number of myelinated nerve fibers were also significantly higher in the nerve-lengthening group than in the autografting group for each evaluation period. It appears that the simultaneous gradual lengthening of both proximal and distal nerve stumps might have potential application in the repair of peripheral nerve defects.