Objectives: To assess the effect of post-operative radiotherapy (PORT) on long term survival in Testicular Seminoma (TS) patients and factors may effect the prognosis of PORT patients. Results: 12957 patients with a median age of 36.00 (13.00-107.00) years were pathologically diagnosed as primary TS. PORT was performed in 3407 patients. Patients with clinical stages I, II, and III testicular cancer accounted for 70.69% (n=9159), 8.30% (n=1075), and 5.72% (n=741) of all patients, respectively. According to results of multivariate Cox proportional hazard model, lower risk of cancer specific mortality was related with PORT in all patients (HR=0.40 95% CI=0.25-0.63 p<0.0001). However, no benefit in survival (p>0.05) was brought by PORT in either clinical stage. Aging, elevated human chorionic gonadotropin and lactate dehydrogenase level were related with higher risk of cancer specific mortality in PORT patients (p>0.05). Furthermore, aging and elevated LDH were inversely related with the prognosis of CSI PORT patients. No significant risk factor was observed in CSII and III PORT patients. Conclusion: PORT can be benefit to the long term survival in TS patients, however, it did not show significant advantage in patients of either clinical stage based on the results of our study. Elevation of human chorionic gonadotropin and lactate dehydrogenase levels and elder age related with higher risk of CSM in PORT patients. Utilization of PORT in the management of TS should be considered comprehensively.