Sclerosing rhabdomyosarcoma (SRMS) is a newly recognized and rare variant of rhabdomyosarcoma. This soft tissue tumor has not yet been reported as a thoracic lesion. We report a case of a 26-year-old woman who presented with a large chest wall tumor. The tumor originated from the right anterior chest wall and protruded into the intra- and extrapleural cavity. A transcutaneous needle biopsy revealed spindle cells in an abundant hyalinized and fibrous stroma. Although the tumor was considered as a malignant soft-tissue neoplasm, a definitive diagnosis could not be established. A wide excision of the chest wall including the second, third and fourth rib and a part of sternum was performed. Histologically, cytoplasmic cross-striations were found in a portion of the tumor cells. The tumor cells were positive for muscle markers, and the tumor was diagnosed as rhabdomyosarcoma consistent with a sclerosing type of rhabdomyosarcoma. Eighteen months after the complete resection, the patient has pleural disseminations but is alive and undergoing chemotherapy. This case highlights the histologic features of a rare form of rhabdomyosarcoma, and emphasizes the importance of awareness of its existence and the utility of skeletal muscle markers in distinguishing sclerosing rhabdomyosarcoma from its mimics.