The most common sites of osteosarcoma in adolescents are the distal femur and proximal tibia epiphysis. The incidence of osteosarcoma in adolescents is high because the epiphysis is not closed and the malignant proliferation of mesenchymal tissues is the cause of osteosarcoma. Adolescents have a high incidence of osteosarcoma because of the malignant proliferation of mesenchymal tissues. Adolescents have a rapid growth and development especially before the epiphyses are completely closed, which is an important stage for osteosarcoma to occur. Osteosarcoma is a serious malignant tumor that grows rapidly and is highly malignant. It may be caused by viral infection, ionizing radiation, or gene mutations that cause malignant proliferation of undifferentiated mesenchymal cells. It mostly occurs in the metaphysis of femur and tibia. The main manifestations are pain, localized mass, limited joint movement, and severe pathological fracture. Therefore, adolescents are the most common age for osteosarcoma, early detection and early treatment.