Abstract: Objective To investigate the expression of CD34 and MMP-9 in osteosarcoma,as well to explore their relationship and clinical significance.Methods CD34 and MMP-9 were detected by S-P immunohistochemical method in 48 cases of paraffin-embedded sections of osteosarcoma.Results The positive rate of CD34 and MMP-9 in human osteosarcoma is 62.50% and 56.25% respectively,significantly higher than that of osteochondroma.The expression of CD34 is significantly associated with the histological grades and lung metastasis(P=0.014,P=0.002).The expression of MMP-9 is significantly correlated with histological grades and lung metastasis(P=0.013,P=0.013).There is a significant correlation between the expression of CD34 and MMP-9(r=0.005,P=0.006).Conditions such as age and sex have no relation with the expression of CD34 and MMP-9.Conclusion CD34 and MMP-9 participate in the carcinogenesis and development of osteosarcoma,and there is synergetic action between them.