Limb-salvage surgery has become more popular than amputation for the treatment of malignant bone tumor because no differences in local recurrence and the 5-year survival rate have been found. However for young patients with sarcoma, skeletal immaturity may be a contraindication to limb-salvage surgery due to the expected leg length discrepancy. If limb-sparing procedure should be impossible for skeletally immature patients, amputation has to be given first consideration. To minimize the functional difficulty from short amputation stump of above knee amputation, we performed lengthening of the amputation stump using ipsilateral tibia. One patient was lengthened 17cm using ipsilateral tibia and the other, 12cm. Two patients and their families were satisfied both clinically and psychologically.