Objective To investigate the influences of survivin down-regulation on cell G2/M phase arrest,apeptosis and sensitivity to carbon ion irradiation. Methods Small interfering RNA (siRNA) targeting survivin mRNA was designed, in vitro chemo-synthesized and transfected into SMMC-7721 cells. Survivin mRNA expression in SMMC-7721 cells was measured by real-time PCR, and the apeptotic rates by Annexin-FTTC at 24 and 48 h after transfection. Cell G2/M phase arrest after transfection was assessed with flow eytometry as well. Cellular sensitivity to high-LET carbon ions was determined by means of colony-forming assay. Results The expressions of survivin at mRNA level were down-regulated to be 59% and 39% in relation to the non-treated cells at 24 and 48 h after siRNA transfeetion, respectively. G2/M phase arrest in SMMC-7721 cells at 24 h after transfection was observed while much more obvious at 48 h. The apeptotic rate of SMMC-7721 cells was 21.41 % at48 h after survivin siRNA transfection, which was significantly higher than that of the cells transfected with negative siRNA. Moreover, a decreased clonogenic survival in siRNA treated group was shown. Conclusion Down-regulation of survivin gene expression in SMMC-7721 cells by siRNA could effectively induce cell apeptosis and G2/M phase arrest, and enhance the cellular radiosensitivity to high-LET heavy ions.