Osteoarthritis (OA) is a common chronic disease causing disability and pain in older adults worldwide. It is characterized by degeneration of articular cartilage, subchondral osteosclerosis, osteophyte formation, cartilage angioge-nesis, and inflammation of the joint. Unfortunately, a series of damages will be caused, such as degeneration of articular cartilage, fracture, defect, and the entire articular surface injury. As the pathogenesis of OA has not been clarified, effective drugs for the patients are almost blank. This article reviews the pathological changes from early stage to late stage of osteoarthritis according to the existing reports.