Introduction: Current treatment in treating patient with osteosarcoma is combination of chemotherapy and surgery, either limb-sparing or limb-ablation surgery. One challenge in limb-sparing technique in children is how to deal with the remaining growth of the bone. We created a limb-sparing reconstruction technique that can be fitted in many types of hospital and have a good functional outcome. Case presentation: We reported a case of 13-years-old female with left knee pain since 8 months prior hospital admission with previous treatment to a bone setter and open biopsy at previous hospital. Histopathological findings demonstrated osteosarcoma. The patient had a neoadjuvant chemotherapy and followed with limb-sparing surgery. We performed wide excision of proximal tibia and reconstruction using a bone on polyethylene hemiarthroplasty system of the knee joint. Patient then continued on adjuvant chemotherapy. Later on, local recurrence occurred and we performed excision again. Within one year, the patient could walk full weight bearing, perform daily activities with no limitation and no pain, and she had MSTS score of 21. Discussion: Limb-sparing surgery remains a challenging procedure in skeletally immature patients. This bone on polyethylene technique would be functional due to high adaptability in paediatric patients in order to decrease the number of surgeries until the final goal of limb equalization. Conclusion: Bone on polyethylene hemiarthroplasty system enables good and reliable functional outcome while maintaining the knee joint for daily activity. It can be chosen as one of viable options in treating osteosarcoma around the knee joint in children.