Objective: To provide the biochemical and histological foundation for the vascularized tendon transfer to the Achilles tendon defect.Methods:Twelve New Zealand adult rabbits were divided into two groups randomly.The Achilles tendon defects were repaired with vascularlized flexor digitorum longus tendon, and the contralateral Achilles tendon served as a free tendon control.The histological observation and biochemical tests were made at 12 weeks after operation.Results: In the experimental sides, the histological structure closed to the normal Achilles tendon and the transfer tendon regained 67.7% of the tensile strength of the normal Achilles tendon.The results of the control sides indicated that the tendon fibre were wrapped by the scar tissue histological, and that the tendon transfers regained 35.3% of the tensile strength.The difference between the experimental group and the control group was significant ( P 0.01).Conclusion: The vascularized tendon transfer is superior to the free tendon transfer in the repair of the Achilles tendon defect.