Abstract: Objective To investigate the serum level of tumor necrosis factor-α（TNF-α） in patients with osteosarcoma pretreatment and its correlation with prognosis. Methods The serum levels of TNF-α in 56 patients with osteosarcoma before chemotherapy and 50 healthy people were detected by ELISA method. The factors affecting the serum TNF-α level of osteosarcoma patients and the correlation of TNF-α with prognosis were also studied. Results The expression of serum TNF-α pretreatment of 56 osteosarcoma patients was （32.08 ± 19.68） pg／ml， higher than （18.00 ± 19.88） pg／ml of the healthy people. There were statistical significances（P=0.04）. The level of TNF-α in osteosarcoma patients was correlated to alkaline phosphatase（P=0.002） and stage（P=0.026）. In osteosarcoma patients， the median overall survival（OS） in elevated TNF-α group（n=44） was 22.2 months， lower than 32.1 months in normal TNF-α group. There were statistical significances（P=0.037）.Conclusion The level of serum TNF-α in patients with osteosarcoma is significantly increased， and is correlated to prognosis. The detection of serum TNF-α has certain value for prognosis and treatment of osteosarcoma.