We report robot-assisted thoracoscopic extended thymo-thymectomy (rThx) for myasthenia gravis (MG) with thymoma. The patient was a 50-year-old woman who complained of right-side ptosis and muscular weakness of the bilateral upper extremities, and a diagnosis of MG (MGFA class IIa) was made after several examinations. She was referred to our hospital for further evaluation and treatment. Chest computed tomography revealed an anterior mediastinal tumor (diameter: 46×35 mm). RThx with a left approach was performed with a surgical system. After three ports and an assist port were placed, CO2 insufflation was performed. At first, fatty tissue was resected around the left phrenic nerve, and from the left lower pole to the upper pole of the thymus was removed. Next, the contralateral pleura was cut and the right phrenic nerve was identified, and from the right lower pole to the upper pole of the thymus was removed. The thymus including thymoma and surrounding fatty tissue were completely removed. The pathological diagnosis was World Health Organization type B2 noninavasive thymoma, and the Masaoka classification was stage I. On CO2 insufflation into the thorax, RThx with a left approach was performed safely with good visualization.