Originating from the synovium, multiple free-floating intra-articular particles, called rice bodies, typically resemble cartilage and have a fibrin structure. While the etiology of rice body formation is unclear, they often occur in rheumatoid arthritis and other seronegative arthropathies; they also occur in tuberculosis, though the incidence is much lower. They are often encountered by rheumatologists or clinical orthopedists. A 33-year-old female who suffered from occasional swelling and pain of her left knee for 3 months was admitted with a mechanically locked knee. Free-floating rice bodies were identified on magnetic resonance imaging (MRI), and arthroscopic intervention was performed for diagnostic and therapeutic purposes. After the removal of all bodies and effusion with mechanical irrigation, an arthroscopic subtotal synovectomy was performed.