Abstract: Objective 　To study the effect s of pSUPER-siRNA-STAT3 gene on the growth of A549 cells. Methods 　Two pairs of DNA template coding siRNA were synthesized against STAT3 to reconstruct pSUPER-siRNA- STAT3. Which was transfected into A549 cells. The STAT3 expression in A549 were transfected with pSUPER-siRNA-STAT3, and it was detected by RT-PCR and cells viability by fluorescence microscope. Results 　The siRNA eukaryotic expression vector against STAT3 mRNA was successfully conct ructed, which was transfected into A549 cells. The level of STAT3 mRNA in A549 cells was inhibited by the specific siRNAs. The decrease of STAT3 mRNA expression began to appear 24 hours after transfection. And the most apparent interfering efficiency was 85. 32 %, 48 hours after transfection, which was markedly higher than that in the cells transfected with the control siRNAs. Both siRNAs from different loci had interfering effect on STAT3 mRNA expression, but there was no significant difference between them. Compared with those control cells, the apoptotic rates were significantly higher in siRNA transfected cells by fluorescence microscope. Conclusion 　pSUPER-siRNA-STAT3 could significantly inhibit STAT3 expression, suppress the growth of A549 cells. The RNA interfering technique targeted on STAT3 may provide a new method in the gene therapy of lung cancer.