Malignant granular cell tumors (MGCT) are extremely rare, representing 0.5-2.0% of all granular cell tumors1) . Surgical excision with a clean margin remains the best possible option as no chemotherapy or radiation has been reported effective. This paper presents a case of a 62-year-old Japanese woman with a malignant MGCT on the left chest wall. She was referred to our hospital because of a mass at the left costal arch in July 2013. A chest computed tomography (CT) scan and magnetic resonance imaging (MRI) scan revealed a tumor (about 5.5cm in diameter) on the left 9th rib within the external oblique abdominis muscle. MGCT was suspected by a percutaneous needle biopsy but not diagnosed definitely. In August 2013, the patient underwent surgical excision of the lesion with a surgical margin of 1 cm. After the excision, histological and immunohistochemical analysis allowed making the definite diagnosis of MGCT. As part of the margin was close to the tumor, the patient underwent additional excision in September 2013. Thereafter histopathology revealed no residual tumor. The patient has been free from recurrence and metastasis as of about 45 months after the operation.