Background At present, amputation was widely adopted for young patients when limb salvage is deemed risky with several surgical strategy such as rotationplasty. However, leg length discrepancies and unfavorable cosmetic results is an indispensable complication of this strategy. The purpose of this study is to demonstrate a novel reconstruction strategy and evaluate the early clinical and functional outcomes of the strategy. Methods Plastic lengthening amputation has been developed by lengthening the stump to preserve one additional distal joint for fixing the artificial limb well. The surgical technique and postoperative management were documented, and the functional outcomes were compared with those of traditional amputation. Six pairs of patients matched for age, sex, location, pathologic type and final prosthesis underwent individually designed plastic lengthening amputation with vascularized autografts or traditional amputation between January 2005 and December 2007. All patients were followed, and the locomotor index and MSTS were used to describe and quantitatively grade limb functional outcomes after amputation. The complications and functional outcomes of the two procedures were compared. Results Twelve patients with osteosarcoma or Ewing sarcoma in either the femur or tibia were included in the study. Six patients underwent plastic lengthening amputations, three of whom also underwent vascular anastomosis. All patients were followed for an average of 48.17 months; bone healing required an average of 3.3 months. No local recurrence was found. The average postoperative locomotor index functional score of the affected limb was 32.67 ± 5.89 in the plastic lengthening amputation group but was 19.50 ± 7.87 in the traditional amputation group. Conclusions Plastic lengthening amputations with vascularized autografts could preserve one additional distal joint and improve the function of the amputated limb in selected bone sarcoma patients. MSTS analysis also indicated that the patients would have better functional outcomes with plastic lengthening amputation than with traditional amputation.