To investigate the adaptive response of low doses of gamma−rays to challenge doses of Mitomycin C(MMC) on the splenic lymphocytes in mammalian, mice were irradiated with inductive doses of 50, 75, 100mGy 6h before challenge dose of MMC (1mg/kg). Observations were made on efficacy of splenocyte count, cell cycle progression, DNA synthesis in number of splenocytes, Flow cytometry, the splenic lymphocyte transformation induced by Con A and LPS. The number of splenocytes in Group B(1mg/kg of MMC) was significantly lower than that the control(Group A). The number of splenocytes in Group C, D and E (50−100mGy + MMC) was significantly higher than that in Group B. Both the percentages of G,0,/G,1, and S phase cells in Group D and E were lower and higher than that in Group B in cell cycle progression of the splenic lymphocyte transformation induced by Con A. Significant changes of the numbers were found in the LPS treated groups (except G,0,/G,1, phase of Group E). The results showed adaptive response of low doses of γ−rays to challenge doses of MMC on number of splenocytes and cell cycle progression of the splenic lymphocyte transformation induced by Con A and LPS in mice.