In this paper the effect of PprI protein of deinococcus radiodurans to protect mice from acute radiation injury had been investigated meanwhile the relative mechanism had also been discussed. After injecting PprI protein or physiological saline into the muscle of mice, the blood cell count and the apoptotic rates of bone marrow cells, spleen cells and thymocyte cells on the 1st, 7th, 14th, and 28th day after irradiation were investigated. Compared with the physiological saline injection group, it has been found that the leucocyte number is significantly higher on the 28th day after irradiation (p<0.05), the platelet number and the lymphocyte ratio is obvious higher on the 1th day and the 7th day after irradiation (p<0.05) in peripheral blood of the PprI protein injection group. On the other hand, the apoptotic rate of spleen cells is significantly lower on the 1th, 7th, and 14th day (p<0.05), the apoptotic rate of thymocytes is significantly lower on the 14th and 28th day (p<0.05), the apoptotic rate of bone marrow cells is significantly lower on the 1st, 14th and 28th day (p<0.05), and the apoptotic rate of bone marrow cells is return to normal level on the 28th day after irradiation. The result indicates that the PprI protein of deinococcus radiodurans can prevent mice from the acute radiation injure apparently.Cited