We report a spontaneous embryonal rhabdomyosarcoma in the abdominal cavity of an aged (88-week-old) Sprague-Dawley rat. The animal had a firm lobulated 5 × 5 × 4.5 cm mass in the abdominal cavity that was whitish to tan with necrotic and hemorrhagic plaques. Microscopically, the mass contained nodules with spindle or globoid shaped neoplastic cells with abundant eosinophilic cytoplasm and round or elongated nuclei mixed with other spindle cells with a filamentous appearance and scanty cytoplasm. Multinucleated cells and cross-striations were also observed. The neoplastic cells were positive for vimentin, desmin, and alpha-smooth muscle actin, especially the small spindle cells.