Abstract: ObjectiveTo determine the effect of Radix Angelicae Sinensis and Radix Hedysari （RAS-RH） on radiosensitivity of human liver cancer H22 cells to heavy ion 12C6+ and its possible mechanism. MethodsThe experiment involved a comparison of proliferation of H22 cells (detected by CCK-8 assay) between four groups: control, drug (RAS-RH), radiation, and combination (RAS-RH+radiation). H22 cells were treated with different doses of radiation alone or radiation followed by RAS-RH. The radiation enhancement effect of RAS-RH on H22 was detected by Colony forming assay. The effect of RAS-RH on the apoptosis of H22 cells was detected by flow cytometry. The influence of RAS-RH on the expression levels of related protein Survivin and Caspase-9 was investigated by Western blot. ResultsRAS-RH inhibited the proliferation of H22 cells, with a time and dose dependency 〔inhibitory concentration 20% (IC20)=(117.60±2.15) mg/L〕. The survival rate of H22 cells decreased significantly with the increase of heavy ion 12C6+. The two survival curves produced by the Graph Pad Prism 5.0 software were clearly separated. The combination group demonstrated smaller shoulder area at low dosage and lower survival rate of cells compared with radiation group, with a sensitization enhancement ratio (SER) of 1.39±0.07. The combination group (100 mg/L RAS-RH+2 Gy) had higher apoptosis rate and Caspase-9 protein expression level, and lower Survivin protein expression level, compared with other 3 groups ( P<0.01). ConclusionRAS-RH has radiation sensitization effect on human hepatocellular carcinoma H22 cells. The mechanism may be related to down-regulation of Survivin protein expression and up regulation of Caspase-9 protein expression.