PURPOSE: This study was designed to know the effect of calcium-sulfate and xenograft on the distracted callus after lengthening. MATERIALS AND METHODS: We had operation of subperiosteal osteotomy and external fixation on the tibial diaphysis of young New Zealand White rabbits(2.0-2.5kg); after 5 days of latency period, 7 mm(1mm/day, 2 times/day) of tibial lengthening was reached in a week. At 1 week after lengthening, the 1st experimental group of 7 rabbits received a pellet of calcium sulfate(Osteoset , Wright medical, USA) in the distraction gap, and the 2nd experimental group of 7 rabbits received 5mm2 of xenogrfat(Lubboc ) in the distraction gap. But, the control group of 7 rabbits did not receive any of above materials. We compared three groups with the changes of radiographic findings at every week and bone mineral ratio(DEXA) at every two weeks. RESULTS: The time to complete consolidation of distraction callus of both experimental group(calcium sulfate;14 weeks, xenograft; 15.4 weeks) was shorter than that of control group(16.9 weeks) in radiographic findings. Maximum value of bone mineral ratio of distraction callus was higher and the time to reach the highest value was also shortened in the both experimental group compared to control group. CONCLUSION: By use of bone substitutes as like calcium sulfate or xenograft in the distraction callus with external fixator, it may be possible to shorten the consolidation period and the fixator-wearing period.