Objective:To investigate the biomechanical properties of deep fascia of leg in response to the Tension-Stress Principle during limb lengthening. Methods:Limb lengthening animal model was established in New Zealand white rabbits using a unilateral external fixator applied with four pins to the medial surface of the tibia and monofocal proximal diaphyseal osteotomy with closed multiple drill holes and osteoclasis between the second and the third pins.Seven days after operation,distraction was initiated at a rate of 1mm/day and 2mm/day in two steps, and proceeded until increases of 10% and 20% in the initial length of tibia had been achieved.The deep fascia samples of 30x10mm were clamped to the Instron 1122 tensile testdevice at room temperature with the constant tensile rate of 5mm/min.After 5 load-download tensile tests,the samples were elongated until rupture.And the load-displacement curves were automatically generated by the apparatus. Results:The normal deep fascia showed typical load-displacement rules of collagenous tissues.And each experimental fascia kept the characteristics.The curves of fascias at the distraction rate of 1mm/day were closer to the curves of normal fascias.For the normal fascias,the ultimate tension strength was avarage 2.69N,and the strain at rupture was avarage 14.11%.And the ultimate tension strength of the fascias after lengthening increased. Conclusion:These results prove that the Tension-Stress during limb lengthening. has great effect upon foe biomechanical properties of deep fascia.The curves of fascias at a rate of 1mm/day and increase of 20% were the closest to the curves of normal deep fascias.