The radioprotecting effects of EGCG on Human HaCat cells of epidermal keratinocytes irradiated by X rays were investigated. MTT assays were used to evaluate the impact of different concentrations of EGCG on HaCat cells for 24, 48 and 72 h to find the optimal concentration. HaCat cells were divided into four groups: control, EGCG treatment, X-ray exposure, and EGCG combined with X-ray. Cell survival rates were analyzed by clonogenic assays. The changes in ROS were measured by the DCFH-DA method, and cell apoptosis was detected with the Annexin V-FITC cell apoptosis kit and the apoptotic fragments were analyzed with DNA fragment analysis. Flow cytometry was employed to analyze cell-cycle progression. An increase of HaCat cell numbers was observed after the HaCat cells were treated with EGCG at 0－50 μmol/L, showing a time-dependent manner, while a high concentration of EGCG inhibiting HaCat cell growth. EGCG (50 μmol/L) increased the cloning efficiency of HaCat cells after radiation. EGCG reduced the apoptosis of HaCat cells by X-ray irradiation, compared with single radiation group, the apoptosis rates of the medicine and radiation group decreased from 9.25% to 7.82%; EGCG reduced the apoptosis fragments of HaCat cells by X-ray irradiation compared with the single radiation group. The G2/M phase arrest population of HaCat cells decreased after X-ray radiation, which was induced by the EGCG pretreatment. EGCG can protect HaCat cells during radiation. Radioprotection of EGCG for the cells from apoptosis is associated with its inhibition of ROS induced by radiation, meanwhile, the decrease of radiation-induced G2/M phase arrest may be involved.Cited