In order to investigate the effects of Quercetin on radiosensitivity of human Uterine Cervix Cancer HeLa cells, MTT assay and clonogenic assay were performed to evaluate the cytotoxicity of Quercetin on the cells. Clonogenic assay was used to observe its effects on the radiosensitivity of the cells. MTT result shows that the inhibition of Quercetin on the cells is in the dose-dependent and time-dependent. And the clonogenic assay result shows that the effect of Quercetin on HeLa cells can be divided into two parts, one for the inhibition of HeLa cells and another for the induction of HeLa cell death. The other clonogenic assay result also shows Quercetin can decrease clonogenic survival rate of HeLa cells exposed to X rays. The study shows Quercetin might enhance the radiosensitivity of the HeLa cell line. And it may provide a useful evaluation to combination of ionizing radiation and Quercetin for cancer patients.