Mediastinal granular cell tumor is an exceptionally rare tumor; there are only a few previously reported cases. We report a 21-year-old man with a granular cell tumor in the right posterior mediastinum. Chest computed tomography scans and magnetic resonance imaging revealed a 15x20 mm well circumscribed, homogeneous mass, which was closely associated with the vertebral column. The T1-weighted magnetic resonance image showed low intensities, and moderate intensities were found on the T2-weighted magnetic resonance image. Gd-DTPA enhancement was remarkable on the tumor surface. The present case differed from ordinary neurogenic tumors in magnetic resonance imaging findings. Thoracoscopic resection of the tumor was performed. The tumor was associated with the sympathetic nerve. Histologic analysis revealed a benign granular cell tumor.