OBJECTIVE To determine the effect of short interference RNA (siRNA) against STAT3 induced inhibition of STAT3 gene expression and on the growth and apoptosis of Lewis lung cancer cells.METHODS pSilencer 2.1-U6 STAT3 siRNA against STAT3-mRNA was synthesized. Lewis lung cancer cells were divided into 3 groups: vehicle,plasmid, and STAT3 siRNA in which the cells were treated with RPMI-1640 culture media, or transfected with pSilencer empty vector, or pSilencer STAT3 siRNA. Semiquantitative RT-PCR and West blot analysis of STAT3 gene expression in the cells was performed 72 h after transfection. MTT assay for cell proliferation, flow cytometry and DNA laddering electrophoresis were used for determination of cell proliferation and apoptosis.RESULTS STAT3 was markedly expressed at both the mRNA and protein levels in the cells treated with RPMI-1640 media or transfected with the plasmid vector, whereas STAT3 expression was significantly reduced in cells treated with STAT3 siRNA. These findings suggest that STAT3 siRNA effectively inhibited STAT3 expression. Transfection of the cells with STAT3 siRNA resulted in significant cellular growth inhibition and enhanced apoptosis.CONCLUSION Transfection of Lewis lung cancer cells with synthetic STAT3 siRNA resulted in effective inhibition of STAT3 gene expression at both protein and mRNA levels, leading to induced apoptosis and growth suppression.