The effect of natural hot and humid environment (HHE) and mock HHE on γ-irradiated mice and their preliminary mechanisms were studied by comparing the survival rate and the median time, etc. The results indicated that: (1) Comparing to the RT-treated mice, there were obvious death rate increase and median time promotion with the mice treated with mock HHE for over 60 min and 7Gy γ-ray irradiation, whereas no difference was observed within the 9Gy groups. (2) The mock HHE treatment had no obvious effect on peripheral blood lymphocyte of the γ-ray irradiated mice, however, lymphocyte of the RT-treated mice achieved minimum on the 3,rd, day after irradiation, whereas the lymphocyte minimum of (3.3±0.3) ×10,7, was achieved on the 5,th, day after irradiation with the HHE-treated mice, with marked difference between the two minimum data. (3) Comparing to the RT-treated mice, the differences in survival time was obvious with the 7Gy groups exposed to entire natural HHE and natural HHE for 9h,. In the 9Gy group, the survival time of the 6 h, 9h and entire natural HHE groups were all significantly shorter than that of the RT group. Descending rate of peripheral blood lymphocyte of the RT group was lower than that of all natural HHE groups, and the lymphocyte fluctuating resuscitation was found in the RT group, whereas no such changes in all natural HHE groups. It is concluded that the mock and natural HHE treatments decreased significantly survival indexes of the irradiated mice, giving rise to increased incipient descending rate of peripheral blood lymphocyte of the mice.