[Abstract] Objective To investigate the significance of expression of MMP-9, IL-6 mRNA and corresponding proteins in Osteoarthritis. Methods Immunohistochemical(IHC) analysis was used to determine the distribution of MMP-9 and IL-6 protein in chondrocytes and synoviocytes of osteoarthritis from 60 patients with osteoarthritis group and 20 patients with normal control group. Expression of MMP-9 and IL-6 mRNA in chondric and synovial tissues was detected in 30 cases with osteoarthritis group and 10 cases with normal control group by in situ hybridization(ISH). Results IOD of MMP-9 mRNA and corresponding protein in OA was significantly higher than normal control group (P<0.01), and there was difference between IOD of IL-6 mRNA and corresponding protein in OA and control group (P<0.05). There were positive correlations both between mRNA and corresponding protein in OA (r=0.924, 0.917; P<0.01). There were also significantly positive correlations both between IOD of MMP-9 and IL-6 in OA detected by ISH and IHC (r=0.426, P<0.05; r=0.444, P<0.01),respectively. Conclusion IL-6 may be up-regulate the expression of MMP-9 of articular chondrocytes and synoviocytes in OA, and both promote the biological behavior of OA such as occurrence,progress,etc.