Abstract: Objective: To investigate the effect of inhibiting the S100A8 gene using siRNA on apoptosis and chemosensitivity of Hec-1B cells in vitro. Methods: Inhibited expression of S100A8 mRNA was achieved after transfection of a vector ex-pressing S100A8 siRNA. Reverse transcriptase polymerase chain reaction (RT-PCR) and Western blot were used to detect the expression of S100A8 mRNA and protein. Apoptosis was detected by flow cytometry as well as fluorescent staining.The inhibitory rates of Cisplatin, Epirubicin and Paclitaxel in Hec-1B cells were detected by MTT assay in vitro. Each drug was administered in two different concentrations. Untransfected Hec-1B cells were used as the control. Results: We found remarkable suppression of the expression of S100A8 in Hec-1B cells transfected with the S100A8 siRNA vector and the effect was maintained for 10 days. The rate of apoptosis was 30.34± 10.30% in transfected cells and 18.14± 2.68%in the controls (P=0.01). The growth of transfected Hec-1B cells was inhibited remarkably by Cisplatin, Epirubicin and Paclitaxel, with a significant difference from that of the controls (P<0.05). Conclusion: RNA interference of the S100A8 gene can inhibit the expression of S100A8 in Hec-1B cells, inducing Hec-1B cell apoptosis and increasing the chemosensitivity of Hec-1B cells. S100A8 may be involved in the mechanism of multidrug resistance in Hec-1B cells.