Objective:To explore the incidence, clinical characteristics, imaging features, clinical outcome and prognosis of indeterminate pulmonary nodules (IPN) in patients with osteosarcoma.Methods:A total of 69 patients of osteosarcoma with IPN in lung treated in the Bone tumor Center of Eastern Theater General Hospital from January 2011 to January 2021 were collected retrospectively, there were 47 males and 22 females, with a median age of 19 years old (range 7-60 years old). The clinical characteristics including disease-free interval, the chemotherapy response, with recurrence/non-pulmonary, IPN presence before / during / after chemotherapy and imaging features of IPN including number of IPN, location of IPN, density of IPN, boundary clarity of IPN and outcome. The patients were divided into the metastasis pulmonary nodules group and the benign nodules group according to the final outcome of IPN. Further, χ 2 test was performed for comparison of the clinical and imaging characteristics between the two groups. The survival of patients was counted and the correlation between single factor and survival was compared by Kaplan-Meier test, and multivariate survival analyses were performed using Cox proportional hazards regression models. Results:Sixty-nine cases occurred IPN in 211 patients with osteosarcoma, with an incidence of 32.7%. Of the 69 patients, 45 patients (65.2%) with IPN were diagnosed as metastases, and 24 patients (34.8%) with IPN were diagnosed as benign nodules. Follow-up length ranged from 1 to 124 months, with the median follow up time 43 months. To the end of follow-up, 41 patients (59.4%) remained alive and 28 patients (40.6%) had died. The median survival time was 41.0 (20.0, 65.0) months and the median survival time after diagnosis of IPN was 25.0 (10.0, 43.0) months. There were significant differences in lung nodule density ( P<0.001), boundary ( P=0.002), history of recurrence/extra-pulmonary metastasis ( P=0.023) and chemotherapeutic effect ( P<0.001) between the metastasis pulmonary nodules group and the benign nodules group. Multivariate survival analysis showed that chemotherapeutic effect was an independent factor affecting the overall survival of patients [ HR=0.048, 95% CI (0.01, 0.26)]. Boundary definition [ HR=0.12, 95% CI (0.02, 0.93)] and chemotherapeutic effect [ HR=0.06, 95% CI (0.01, 0.29)] were independent factors influencing survival after diagnosis of IPN. Conclusion:Osteosarcoma patients with IPN have a poor prognosis. The poor effect of chemotherapy is an independent risk factor for the overall survival time of those patients and the survival time after diagnosis of IPN. The boundary definition of IPN is an independent risk factor for the survival time after diagnosis of IPN.