Rhabdomyosarcoma is the most common soft tissue sarcoma in childhood and acounts for 6% to 15% of all cases of childhood cancer, Rhabdomyosarcoma in seventh most common form of childhood neoplasms, following acute leukemia, tumors of the central nervous system, lymphoma neuroblastoma, Wilm`s tumor, bone tumor. Rhabdomyosarcoma can arise anywhere in the body, but primary site in the thorax is relatively rare. We experienced a case of aveolar rhabdomyosarcoma arising from intercostal muscle, A 12 year-old woman was suffered from the intermittent left chest pain radiating to the scapular area and dyspnea, On physical examination, pulmonary friction rub was heard on the left upper lobe area. Qn adimission, the chest simple radiography revealed a 7 x 6, 5cm sized radio-opaque mass with pleural effusion in the superior mediastinum and the CT showed a well difined radio-opaque mass including the destructed 2nd rib and pleural effusion. The percutaneous tra-nsthoracic needle aspiration biopsy was likely to show blastoma. After the chemotherapy[vincristine, actinomycin-D, cyclophosphamde] was done to treat blastoma, the pleural effussion was subsided and the mass was slightly decreased by 4.5x 4. 5cm. For treatment and diagnosis, we performed en-bloc resection and the defected chest was reconstucted with Gortex patch. Grossly, the specimen was colored graysh-white and arised in between two ribs The microscopic findings showed that the tumor cells were small round with scant pinkish cytoplasm on the H-E stain and the tumor cell nests were grouped by reticulum fibers and showed alveolar pattern on the silver stain The electromicroscopic finding presented that the cytoplasm contained tangled fibrillar and flocculent materials. The histopathologic findings were compatable with laveolar rhabdomyosarcoma. She was discharged without any complication. After discharge, she has been treated with radiation theraphy and chemotheraphy, and not recurred untill last follow-up We report a case of alveolar rhabdomyosarcoma arising to intercostal muscle, developed in 12 year-old waman, with brief review of literatures.