This experiment was carrid out to investigate whether Aloe arborescens had a radioprotective effect in cobalt-60 gamma irradiated(600 and 700ra4s) mice. The survival ratio of mice for 30 days and blood pictures were investigated. 1. The survival ratios of 600ra4s gamma Irradiated(dose rate 50rads/min.) in pre-irradiation aloe administered group(A), post-irradiation aloe administered group(B) and control group were 73.3%, 72.3% and 63.3%, and those of 700ra4s groups were 63.3%, 60.0% and 51.7%, respectively. 2. The total leucocyte counts of aloe administered groups were less decreased and more rapidly recovery to normal level than those of control group. 3. The lymphocyte counts were rapidly decreased on the 1st day after irradiation in all experimental groups than those of control group. 4. The recovery effects of total leucocyte counts of pre-irradiation aloe administered groups were superior to those of post-irradiation aloe groups and control group.