Objective：To investigate the effect and the mechanisms of lentiviral-shRNA-mediated signal transducers and activators of transcription 3（STAT3） silencing on the chemosensitivity to 5-fluorouracil（5-Fu）， of human gastric cancer cells SGC-7901. Meth－ods：The shRNA sequences targeting STAT3 was constructed and lentiviral vectors was used to transfect human gastric cancer cells SGC-7901. The interference effect of STAT3-shRNA was detected by real-time PCR and Western blot. The chemosensitivity to 5-Fu was analyzed by MTT assay and the flow cytometry was used to examine cell apoptotic rate. Western blot was used to compare the ex－pressions of anti-apoptotic proteins Bcl-2，Mcl-1，survivin. Results：Lentiviral vectors containing shRNA targeting STAT3 gene were successfully established and transfected into SGC-7901 cells．Real-time PCR and Western blot analysis showed that the STAT3-shRNA significantly inhibited the mRNA expression by 54% and protein expression by 40%（P<0.05）． The inhibitory rate of cell pro－liferation and the apoptotic rate were obviously higher in the cells treated by STAT3-shRNA（P<0.05）. STAT3-shRNA also induced downregulation of the anti-apoptotic proteins Bcl-2，Mcl-1 and survivin（P<0.05）. Conclusion：In summary，STAT3-shRNA could effectively inhibit the proliferation and accelerate the apoptosis of SGC-7901 cells，leading to the enhancement of their sensitivity to 5-Fu. The mechanism may be related with block of STAT3 signaling pathway though inhibiting STAT3 activation，thus decreasing ex－pressions of its downstream anti-apoptotic proteins Bcl-2，Mcl-1 and survivin.