Abstract: Objective To investigate the radiosensitivity enhancement of ginsenoside Rg3 on esophageal carcinoma EC109 cells. MethodsThe survival rates of EC109 cells at 24，48 and 72h after treatment with different concentrations （10， 20， 50， 100， 200， 400， 600mmol/L） of Rg3 were determined by MTT in vitro. The cloning formation assay and multi-target singlehit model were employed to calculate the sensitization enhancement ratio （SER） after pretreatment of 10 mmol/L Rg3 following irradiation of 0， 1， 3， 6 and 9Gy. According to the experimental protocol， the following experiments were carried out in control group， irradiation group and Rg3+irradiation group. The apoptosis rate and DNA damage were evaluated by flow cytometry and Foci focus formation assay in the 3 groups after 48h irradiation of 8Gy X-ray. Results The Rg3 ranging from 10 to 600mmol/L could reduce the survival rates of EC109 cells in a doseand timedependent manner. The SER of 10mmol/L Rg3 for EC109 cells was 1.28. The apoptosis rate of Rg3+irradiation group was （62.33±4.60）%， higher than （6.46±1.23）% of control group and （30.68±3.55）% of irradiation group with significant difference（P＜0.05）. The number of Focipositive cells in Rg3+irradiation group was 64±12， higher than 6±3 of control group and 32±6 of irradiation group with significant difference （P＜0.05）. ConclusionRg3 can exert radiosensitizing effect on esophageal carcinoma EC109 cells，inhibite cell activity and induce cell apoptosis and DNA damage.