Abstract: Objective To explore the effect of MSH3 knock-down on sensitivity of tongue cancer cells to cisplatin. Methods Three small interfering RNA (siRNA) fragments targeting MSH3 CDS region were synthesized and transfected into CAL27 cells via Lipofectamine. Real-time PCR and Western blotting were used to assess the efficiency of MSH3 silencing. MTS, apoptosis staining and cell immunofluorescence assay were used to examine the cisplatin sensitivity, apoptosis and DNA repair of transfected CAL27 cells. Results One of the 3 siRNAs was found to significantly reduce the expression of MSH3 protein in CAL27 cells (P<0.05). MTS assay showed that MSH3 silencing resulted in an significant reduction of IC50 of cisplatin from 21.32 to 13.95 μmol/L (P<0.05) and increased the apoptotic index of the exposed cells from 4.23±1.27 to 11.32±1.82 (P< 0.05). Immunofluorescence assay demonstrated that silencing MSH3 markedly reduced the number of γ-H2AX foci. Conclusion Silencing MSH3 can significantly increase cisplatin sensitivity of tongue cancer cells, the mechanism of which involves mainly attenuation of repair of DNAdouble-strand damage in the cells.