Objective To investigate the clinical manifestations and potential prognostic factors of neuroendocrine tumors of the thymus (NETT).Methods The clinical data of 139 patients with pathologically confirmed NETT from the Surveillance,Epidemiology,and End Results (SEER) database in National Cancer Institute between January 2007 and December 2014 were retrospectively analyzed.Cox proportional hazard regression was used to assess the prognostic influencing factors of NETT.Results The median age at diagnosis of 139 patients with NETT was 59 years old,and age was (58±17) years old.There were 95 males and 44 females,and the ratio was 2.2 ∶ 1.The median overall survival time was 90 months.Univariate analysis showed that the tumor stage (P =0.001),the tumor grade (P =0.001) and the surgery (P =0.003) were associated with prognosis.Multivariate analysis showed that the tumor grade was the independent prognostic factor for the patients with NETT (HR:5.70;95％ CI 1.75-18.58;P =0.004).Conclusion NETT is a rare malignancy with tremendous aggressiveness.Tumor grade is an independent risk factor for the prognosis of the patients with NETT,and the prognosis of well-differentiated patients is better than that of poorly differentiated patients.