This is a case of synovial chondromatosis which affecting the knee joint of a fifty-four-year old man. Chief coomplaints were limited knee joint motion and foreign body sensation of almost 20 years duration. Two walnut sized hard masses were palpable, one at the infra-patellar region and the other at the supra-patellar region, and they revealed as radio-opaque loose bodies radiologically. The loose bodies, measured 5×4×3, 3×2×1.5, and 4×3×2 cm., were removed surgically, and found to have the pedicles from the synovial membrane. The diagnosis of the synovial chondromatosis was confirmed by pathological study. The post-operative course was uneventful and three months later from the operation, the patient had the good range of the knee joint motion.