Abstract: Objective To investigate the survival and prognosis related factors of osteosarcoma patients with lung metastasis suffering spontaneous pneumothorax. Methods The data of 14 metastatic osteosarcoma patients with spontaneous pneumothorax and 40 osteosarcoma patients without spontaneous pneumothorax were reviewed. Survival analysis was performed by Kaplan-Meier method. A Cox regression model was utilized to analyze risk factors affecting the prognosis of metastatic osteosarcoma. Results Fifty-four metastatic osteosarcoma patients were all followed up. The median progression free survival（PFS）and median overall survival（OS）were 2 months and 11 months，respectively，and the 2-year survival rate was 14.3％.In 40 patients without spontaneous pneumothorax，those data were 2 months，16 months and 35.0％. The difference of OS between patients with／without spontaneous pneumothorax was significant（P＜0.05）. Cox regression model revealed that number of lung metastatic lesions and spontaneous pneumothorax were indepengdent factors affecting OS（HR=0.34，95％CI：0.15-0.79，P=0.01；HR=0.8，95％CI：0.16-0.87，P=0.02）. No correlation was found between the incidence of spontaneous pneumothorax, PFS and chemotherapy. Conclusion In osteosarcoma patients with lung metastasis，spontaneous pneumothorax is associated with poor prognosis compared with those without this complication.