To search for the opportunity for assessing doses as a biological dosimeter, an approach was estab-lished for detecting the expression levels of γ-H2AX in peripheral blood lymphocytes by flow cytometry. The peripheral blood from health donors irradiated in vitro by 60Co γ-rays. The geometric mean fluorescence intensity values of γ-H2AX in lymphocytes labeled with anti-γ-H2AX-antibody by using indirect immunofluorescence were analyzed by flow cytometry, and the relative fluorescence intensity was calculated. The geometric mean fluorescence intensity values and the relative fluorescence intensity of γ-H2AX in intracellular effect were compared between the different instruments type and parameters setting. Two dose-response curves were established and compared 30 min post-irradiated when the geometric mean fluorescence intensity and the relative fluorescence intensity of γ-H2AX in lymphocytes were used as the indicators. The geometric mean fluorescence intensity was obviously affected by different instruments type and parameters setting after irradiation with various doses, but the relative fluorescence intensity of γ-H2AX in lymphocytes did not significantly correlate with the different instruments type and parameters setting after irradiation with various doses. The relative fluorescence intensity as the indicator analyzed by flow cytometry might improve the stability and repeatability, so this new approach would be a potential biological dosimeter.Cited