In order to identify the radiosensitivity-related genes，microarray technology was used for candidate genes screening and it was identified that IER5 (Immidiate early response 5) could be up-regulated after radiation. Biological relationship between IER5 and radiation was investigated, and its biological function was examined in human cervical carcinoma treated with radiation. RNAi technology was employed to knock down IER5 gene in HeLa cells and establish the stable transfected cell lines, IER5-siRNA-HeLa. It was found that there was more S/G2/M phases cells with larger size in IER5-siRNA-HeLa cells than that in the control cells when treated with irradiation. The results indicated that IER5 might be involved in cell growth and proliferation. Most importantly, IER5 knockdown increased the radioresistance in cells, which indicated IER5 might be a potential target for the radiotherapeutical treatment in the cervical carcinoma.