Limb salvage operation was introduced to treat, low grade malignant bone tumors about 100 years ago. However, amputation has been the most popular choice for primary malignant bone tumors. Recent improvement of chemotherapy, diagnostic methods and surgical techniques enabled us to treat more malignant bone tumors such as osteogenic sarcoma with limb salvage operation. 6 cases of malignant bone tumors were treated with wide resection and tumor prosthesis from Oct., 1987 to Jan., 1989 at Dept. of Orthopedic Surgery, Seoul National University Hospital. 4 cases of osteosarcoma, 1 case of parosteal osteosarcoma and 1 case of chondrosarcoma were identified. MRI was useful for determining the extent of tumor and surgical planning. All the patients osteosarcoma had neoadjuvant chemotherapy. The mean follow-up was 14.5 months ranging from 8 to 22 months, and theirresults are so far good except one pulmonary metastasis and one local recurrence. We present this as a preliminary report.