Objective To Investigate the stress adaptability of freeze-dried bone allograft. Methods Cortical and cancellous allograft were transplanted to each side of the midshaft diaphyseal ulnar respectively in each group of 28 animals. The left transplanted allograft was free from fixaton and bear normal physiological load, while the right transplanted allograft was protected from loading by a simple external fixator and bear less load. Animals were killed in batch at 2nd, 4th, 8th, 16th week after transplantation and specimens were taken out for bone histomorphometry study and analysis of collagen gene expression by in situ cDNA-mRNA hybridization.Results Labeled surface(LS) and bone mineral apposition rate(MAR) of the normally loaded graft-host bone interface were significantly higher than that of the less loaded side at the 4th,8th,16th week after transplantation. The parameters reflecting the internal repair process of allograft such as LS in cortical and cancellous boen or MAR in cortical bone of the normally loaded side were significantly higher than that of the less loaded side at 16th week after transplantation. The result of in situ hybridization indicated that more osteoblast-like cells with expression of typeⅠcollagen gene occuring in the interface or interior of normally loaded graft. Conclusion The stimulus of physiologic load can accelerate the early union of allograft-host bone interface and later new bone creeping substitution to the necrotic allograft.