Abstract: Objective To study the effect of hot and humid environment (HHE) on the bone marrow and spleen in mouse exposed to γ irradiation. Methods After exposure to γ irradiation at the dosage of 6.5 Gy, the mice were subjected to treatment in HHE for 1 h or at room temperature (RT) respectively. After exposure to HHE, the mice in HHE group were kept at RT. The bone marrow and spleen of the mice in both RT and HHE groups were examined at 1, 3, 5, 9 and 15 days after irradiation for bone marrow cellularity, DNA content in the bone marrow cells, and spleen/body weight ratio. Results Compared with the RT group, mice in the HEE group showed aggravation of decreases in bone marrow cells, DNA content and spleen/body weight ratio. Conclusions HHE aggravates radiation injury of the bone marrow and spleen in mice.