A low-grade fibromyxoid sarcoma (LGFMS), an Evans tumor, is highly unusual. It is rarely described as a primary neoplasm in the thoracic cavity. We experienced a case of a 20-year-old woman with a right intrathoracic tumor that was surgically treated. Postoperative pathology of the resected specimen revealed the tumor to be LGFMS based on its histological appearance, immunohistological staining, and evidence of fused in sarcoma (FUS) translocation by fluorescence in situ hybridization. Tumor resection was performed with a free surgical margin, and the resultant chest wall defect was repaired using prosthetic mesh. The patient has been well without any recurrence for 18 months since surgery.