Gauzoma is a well-known complication in surgical practice. It can mimicsoft-tissue sarcoma clinically if it progresses rapidly. We described a 22-year-old patient who presented with a solid mass over the right knee following ACLrepair sincw one year ago. It was diagnosed to be sarcomatous neoplasm clinically and radiographically because of rapid growth and certain MRI finding. At surgical excision, it was found to be a foreign body granuloma(gauzoma or gossypiboma) intraoperatively and was confirmed by pathologic report. It is a rare orthopaedic condition, often occurred in pelvic and spinal surgery. This case report can offer more information concerning radiographic findings of gauzoma and learning how to detect such foreign body granuloma earlier.