OBJECTIVE To study the early biological parameter changes of blood and immune systems of mice after 60Co γ-ray irradiation in order to find sensitive and reliable biological dose markers for radiation pretreatment of hematopoietic stem cell transplant recipients. METHODS Pure strain BALB/c male mice were randomly divided into control group and three irradiation groups and absorbed doses of total body irradiation by ⁶⁰Co γ-ray were 0, 2, 4, 6 Gy, respectively. In 24h after irradiation, WBC counts and lymphocyte percentages of peripheral blood were determined by blood cell counting; polychromatic erythrocyte micronucleus（mn- PCE） of peripheral blood and bone marrow were observed by microscope after Giemsa staining; apoptosis rates of bone marrow, spleen, thymus cells were assayed by flow cytometry using Annexin Ⅴ and PI double staining. RESULTS Compared with the control group, WBC counts and lymphocyte percentages of peripheral blood in the irradiated groups significantly decreased with the increase of radiation doses（P<0.01），and their regression equations were E=0.1750D2-1.7440D+5.2020 and E=84.9390-3.4255D respectively. The mn-PCE of peripheral blood and bone marrow in the irradiated groups significantly increased with the increase of radiation doses（P<0.01）, bone marrow mn-PCE was positively correlated with the radiation dose with regression equation as E=3.9725D+2.9700. The early apoptosis rates of bone marrow cells, spleen and thymus cells significantly increased with the increase of radiation doses（P<0.01）, which were positively correlated with radiation doses, and their regression equations were E=3.42D + 8.36, E=3.0645D + 3.1840 and E=2.5620D + 2.5090 respectively. CONCLUSION Peripheral blood lymphocyte count and bone marrow mn-PCE rate were linearly correlated to radiation doses, which could be used as sensitive and reliable early biological markers of the radiation pretreatment recipients, and the doses of the radiation pretreatment recipients could be accurately judged according to their regression equations. The early apoptosis rates of bone marrow, spleen and thymus cells were positive linear correlation with the radiation doses, and their regression equations could be used to judge the degree of inhibition of the immune system for radiation pretreatment recipients.