Abstract: Objective To investigate the role of small interfering RNA(siRNA) targeted to survivin in combination with 5-fluorouracil(5-FU) in inhibiting the proliferation of MCF-7 cells.Methods A siRNA targeted to survivin was synthesized and transfected into MCF-7 cells via lipofectin.Changes of the cell growth activity in response to combined treatment with survivin siRNA and 5-FU or 5-FU treatment alone was evaluated by MTT assay.The Q method of Jin Zhenjun was used to evaluated synergism between the synthesized siRNA and 5-FU.Results Treatment with 5 nmol/L siRNA reduced the IC50 of 5-FU from 4.42 to 1.18 μg/ml,and the inhibitory effect of combined treatment on MCF-7 cells was higher than that of 5-FU alone(F=26.74,P<0.01).Synergism effect(Q≥1.15) was observed between 5-FU at lower concentrations and survivin siRNA.Conclusion siRNA may enhance the effectiveness of 5-FU in inhibiting the proliferation of MCF-7 cells.