Recently limb-salvage operation is widely used for the treatment of malignant bone tumor. But distal leg is out of range of limb-salvage operation due to its technical problem. We report satisfactory limb-salvage operation with tumor prosthesis in 3 cases of osteosarcoma of the distal tibia and fibula. Two cases involved in the tibia and 1 case in the fibula. Average age at operation was 23 years. Neoadjuvant and adjuvant chemotherapy were performed in all 3 cases. We used custom made tumor prosthesis which is designed by Seoul National University Orthopaedic Department. Overall Functional Evaluations by Enneking rating system were good in all 3 cases. All cases are CDF(continuosly disease free since the surgical procedure) state at mean follow-up 2 year and 9 months. In conclusion limb-salvage with tumor prosthesis is useful treatment modality for malignant bone tumor of distal tibia and fibula. Good functional results and few complications suggests limb salvage of distal lower leg may be replaceable with B-K amputation.