The giant intra-articular osteochondroma of the knee is very rare and is probably result of synovial metaplasia of the fibrous capsule or of the adjacent connencive tissue of a joint, and of the fragment of articular cartilage. The gross findings and histology are consistent with the osteochondroma. The authors experienced a case of giant intra-articular osteochondroma of the right knee in a 19 years old man who had history of knee injury when he was 16 years old. The mass was excised and the symptome was relieved.