Objective According to heparanase's gene sequence of gene bank,to construct heparanase gene-targeted small interfering RNA(siRNA)and its expression vector and observe its interference effect on the expression of heparanase gene in human malignant breast cancer MDA-MB-231 cells.Methods Heparanase gene-targeted hairpin siRNA was designed,and inserted into pGPU6/GFP/Neo plasmid,which was identified by sequencing.Human malignant breast cancer MDA-MB-231 cells were transfected with the constructed vector using lipofectamine method.FIuorescence photographs were taken.Proliferation inhibition rate of cells was analyzed by MTT assay.Results Three groups of heparanase gene-targeted hairpin siRNA were designed,and inserted into pGPU6/GFP/Neo vector after annealing.Vectors containing siRNA were right by sequencing.Fluorescence photographs showed that MDA-MB-231 cells were transfected successfully by lipofectamine method.MTT showed that proliferation inhibition rate of MDA-MB-231 cells were increased significantly in heparanase gene-targeted groups.The proliferation inhibition rate wag 58.25±3.42,43.70±2.44,39.40±2.38,obviously higher than in blank group(4.48±2.28,P＜0.05).Conclusion Heparanase gene-targeted siRNA and their vectors were successfully constructed.They can promote apoptosis of MDA-MB-231 cells after transfection.