Proteoglycan 4 is a surface-active mucinous glycoprotein secreted in the synovial joint that plays an important role in cartilage integrity. Arthropathy occurring in patients with joint trauma, inflammatory arthritis or genetically mediated proteoglycan 4 deficiencies have insufficient Prg4 to prevent damage to articular cartilage. Recent studies indicate that Prg4 plays a role in preventing damage to the superficial zone and preservation of chondrocytes.It is being used as a new biological therapeutic protein in the treatment of osteoarthritis. This article reviews the structure and function of proteoglycan 4 and its role in the treatment of osteoarthritis.