The changes of cell cycle progression in mice bone marrow hemopoietic cell and the dose-effect relationship after X-ray whole body irradiation (WBI) were studed by flow cytometry (FCM). The data showed the elevation of the percentage of cells in G,1, phase 12h after irradiation (,p,<,0.05), the decrease of cells in S phase 4h (,p,<,0.05) and the increase of cells in G,2,+M phase 4h and 12h after 2.0Gy WBI. 12h after 0.5~6.0Gy irradiation the percentage of cells in G,1, phase became higher than that of sham-irradiation, especialy in 1.0, 2.0, 4.0 and 6.0Gy groups ,(p,<, 0.05 ~,p,<,0.01), both the decrease of S phase percentage (,p,<, 0.05 ~,p,<,0.01)and the increase of G,2,+M phase ,(p,<, 0.05 ~,P,<,0.001) was in a dose-dependent manner. Our results suggested that 2.0Gy X-ray WBI to mice might induce the arrest in G,1, and G,2, phase and the suppression of DNA synthesis, these changes were all in dose- dependent manner within 0.5~6.0 Gy.