Objective To investigate the feature and regularity of the collagen change in bone healing during bone lengthening. Methods Bone lengthening model was made in the middle segment of the rabbit tibia. Five days after the model was established, the bone was lengthened 1.5 mm perday for 14 days. The rabbits were put to death after elongation, 7,14,21,30,40,50,60 and 70 days after elongation. The distracted area of the bone was imbedded with paraffin. After being stained by the picric acidsirius red staining, the slice was observed under polarized microscope. Results The features of the collagen change in the distracted bone were as follows: ① In the fibrous tissue of the distracted area during lengthening period and the early stage after lengthening, there was not only collagen Ⅲ but alsomuch collagen Ⅰ. ② Collagen Ⅰ, Ⅱ and Ⅲ were observed in the cartilage. ③ Collagen Ⅰ, Ⅱ and Ⅲ were also observed in the pseudogrowth plate. ④ Collagen Ⅰ took the dominance during lengtheningperiod and the late stage after lengthening. Conclusion New bone formation in bone lengthening is under the distracted force, so the collagen changes have different features compared with that in fracture healing. Collagen Ⅰ, Ⅱ and Ⅲcan be identified by picric-acid-sirius red staining and polarized microscope, so a new method for studying the collagen typing in bone repairing is provided.