Abstract: OBJECTIVE To select the siRNA which could most effectively inhibit the expression of COX-2, and to observe the change of COX-2 expression in cells. METHODS Three siRNAs were designed(siRNA₂₄, siRNA₉₅₄, siRNA₁₅₅₃) and one FAM fluorescence-labeled siRNA was used as a negative control(HK). Detect the effect of inhibition by RT-PCR and Western blot after transfecting human gastric cancer cell line SGC-7901. RESULTS The 50 μmol·L^-1 Lipofectamine2000 had highest transfection effiency. The expression of human COX-2 gene was suppressed specific and effectively by siRNA₉₅₄, compared with other groups(P<0.01). CONCLUSION siRNA954 can inhibit COX-2 expression effectively. It plays an important role in the treatment of tumor.