Background: Prognostic factors and efficacy of chemotherapy remain unclear in patients with advanced thymic carcinoma. Methods: We performed a multi-institutional, retrospective study named NEJ023 for patients with advanced thymic carcinoma, excluding thymoma type A/B. The patients with no indication for curative treatment were treated with chemotherapy from 1995 to 2014 at 40 institutions of the North East Japan Study Group (NEJSG). Data obtained from medical records included demographic, clinicopathologic, treatment, and outcome information. The Kaplan–Meier method was used to calculate overall survival (OS), and the Cox proportional hazards models were used to adjust for potential confounding factors. Results: Among 324 patients recruited, 289 patients were enrolled in this analysis. Patient characteristics were: median age 61 years (range 14–84); male/female 71%/29%; PS 0–1/2–3/unknown 87%/11%/2%; Masaoka stage IVa/IVb/postoperative recurrence/other 26%/50%/18%/6%; UICC TNM stage IV/postoperative recurrence/other 77%/18%/5%. The predominant histological type was squamous cell carcinoma (66%), followed by undifferentiated carcinoma (12%). First-line chemotherapy included platinum-based doublets in 62% of the patients, monotherapy in 4%, other multi-agent chemotherapy (e.g., cisplatin, doxorubicin, vincristine, and cyclophosphamide: ADOC) in 34%. The median follow-up time was 25.9 months, and median OS from the start of chemotherapy was 30.7 (95% confidence interval, 25.9–35.9) months. There was no significant difference in OS among the different chemotherapy regimens. Age > 75 years (p = 0.011), Masaoka stage IVa (p< 0.001), and volume reduction surgery (p= 0.005) were independent prognostic factors in the multivariate analysis of OS. Conclusions: This is the largest study describing the outcomes of advanced thymic carcinoma in chemotherapy patients. Although Masaoka staging is useful in patients with advanced thymic carcinoma, most of Masaoka stages IVa and IVb patients are classified as stage IV in UICC TNM classification. Volume reduction surgery might prolong OS in advanced thymic carcinoma patients. Clinical trial information: UMIN000015649.