BackgroundRice body synovitis (RBS) is a rare disease. It is prone to be developed due to rheumatoid disorder or tuberculosis infection. Additional infectious arthritis (non‐tuberculous mycobacterial infection and fungal infection), juvenile arthritis, the onset of adult Still's disease, systemic lupus erythematosus (SLE), seronegative arthritis, and non‐specific arthritis. The clinical imaging, histopathological features, and surgical treatment process of a patient were documented combined with literature. Furthermore, differentiation was performed with additional synovitis diseases so that the cognition of synovitis could be enhanced for clinical reference.Case PresentationThe present study reported a 50‐year‐old female patient who suffered from intermittent left knee pain with limited movement for 9  years. The conditions were aggravated after long‐term standing or walking and remitted after taking a rest, accompanied by noose and jamming. The specialist range of motion (ROM) examinations of the left knee revealed: 30° ‐ 0° ‐ 110° and left McMurray sign (+). Plain MRI scanning revealed that in the left knee cavity and the popliteal fossa area, a large number of low signals on free rice‐like bodies were visible inside and the lower femur and the upper tibia exhibited abnormally high signals of patchy lipography. Surgical exploration revealed numerous rice‐like free bodies in the suprapatellar bursa, the intercondylar fossa, and the posterior articular capsule. The patient presently has resolution of symptoms after surgical treatment.ConclusionsThe RBS of the knee joint is very rare in the clinic. As MRI examination can provide valuable information, clinicians should actively perform MRI examination. Once the disease is diagnosed by examination, surgery is the optimal treatment.