Background Robot-assisted thymectomy (RT) has been increasingly performed for treating anterior mediastinal masses. The aim of this study was to compare the early and long-term outcomes between RT and transsternal thymectomy (ST). Methods A total of 429 patients who underwent surgical resection of anterior mediastinal masses were included in this study. RT was performed in 117 patients (27%). Propensity score matching was performed between RT and ST, and 100 patients were selected for each group. Results RT and ST were performed for anterior mediastinal masses, including thymic epithelial tumor and mediastinal cysts. Thymic epithelial tumor was the most common type of tumor, and distribution of pathologic stages was not significantly different between RT and ST (41% versus 39% in stage I, 46% versus 50% in stage II, 9% versus 5% in stage III, and 4% versus 5% in stage IV, p = 0.96). The RT group had significantly less intraoperative blood loss (100.9 ± 105.4 mL versus 354.5 ± 412.4 mL, p < 0.001), lower incidence of postoperative complication (1% versus 12%, p = 0.002), and shorter length of postoperative hospital stay (2.5 ± 1.2 days versus 6.4 ± 6.6 days, p < 0.001) compared with the ST group. Three-year overall survival rates and freedom from recurrence were not significantly different (100% versus 100%; p = 0.88 and 92% versus 99%, p = 0.12) between RT and ST. Conclusions RT demonstrated excellent early outcomes compared with ST, and RT could also achieve comparable long-term oncologic outcomes with ST in thymic epithelial tumor. Therefore, RT should be considered as an alternative surgical option for treating anterior mediastinal masses.