Objective Platelet-rich plasma (PRP) can promote the repair of soft tissue, wound, and bone defect. To investigate the effect of PRP on synovitis by establ ishing papain-induced osteoarthritis model of rabbit knee and interfering withPRP. Methods Twenty healthy 6-month-old rabbits (male or female, weighing 2.5-3.5 kg) were randomly divided into theexperimental group (n=10) and the control group (n=10). The whole blood (10 mL) was extracted from the central aural artery and PRP was prepared with the Landesberg’s method. Meanwhile, the platelet derived growth factor (PDGF), transforming growth factor (TGF), and vascular endothel ial growth factor (VEGF) concentrations in the circulating blood and PRP were measured. The 4% papain solution (0.3 mL) was injected into the knee joint cavity to establ ish the osteoarthritis model. After that, PRP (0.3 mL) was injected into the knee joints every week for 10 weeks in the experimental group, while normal sal ine of the same volume in the control group. At 2nd, 4th, 6th, 8th, and 10th weeks after the first injection, the erythrocyte sedimentation rate (ESR) and interleukin 1β (IL-1β) concentrations in the whole blood were tested, and the histological changes of the synovium were observed by HE staining and the Mankin scores were made. Results The blood cell counting showed that the platelet concentration of PRP was 6.8 times as that of the circulating blood. PDGF, TGF-β, and VEGF were 5, 8, and 7 times as those of the circulating blood, showing significant differences (P lt; 0.05). All animals survived to the end of experiment. There were significant differences in the ESR at 2nd, 6th, 8th, and 10th weeks and in the IL-1β at 4th, 6th, 8th, and 10th weeks between 2 groups (P lt; 0.05). In the control group, the synovium was edematous and thickened with fibrous effusion and pannus on surface; in the experimental group, the effusion of the synovium was decreased and less congestion and edema were observed at the 2nd week; the synovium was observed to be a bit thickened without obvious edema, with sl ight amount of yellowish joint fluid on surface and no conglutination at the 10th weeks. There were significant differences in the Mankin score at 4th, 6th, 8th,and 10th weeks (P lt; 0.05) between 2 groups. Conclusion PRP is beneficial to the alleviation of synovitis induced by papain according to restoring the damaged tissue and depressing the inflammatory factors.