Objective: To explore the mechanism of action of Juanbi Capsules (蠲痹胶囊),a Chinese medicine for invigorating the kidney and replenishing qi,in preventing osteoarthritis of the knee in rabbits.Methods: Seventy-two 4-month-old,Japanese long-eared white rabbits were randomly divided into 6 groups:control (group A),model (group B),Chinese drug; high-dose (group C),Chinese drug; mid-dose (group D),Chinese drug; low-dose (group E),and drug control (group F).With the exception of the rabbits in group A,each rabbit was subjected to plaster cast fixation for 6 weeks to induce osteoarthritis.In addition,rabbits were administrated with an intragastric injection of the Chinese drug (groups C,D and E) or an aminoglucose hydrochloride capsule (group F) for 4 weeks.Blood was drawn from the central ear artery for serum MMP-2 and MMP-9 concentrations,and the knee joint cartilage was harvested for gross observation and light microscopy.Results: There were significant differences in serum MMP-2 and MMP-9 concentrations between group B and groups C,D and E (P＜0.05),with no significant differences between groups D and F.Histological results showed various changes in tissue staining with treatment,with osteophyte and bone cyst formation,and superficial erosion in the articular surface of the cartilage; in some cases,the defect reached the mid-layer of the cartilage,and these changes were lower than those in the model group.Conclusion: Juanbi Capsules assist in preventing osteoarthritis in the rabbit,possibly by decreasing serum MMP-2 and MMP-9 levels.