The research focused on stimulating effect of low doses of ionizing radiation (137Cs γ-quanta) on Saccharomyces cerevisiae was performed. The yeast culture was contained in the nutrient medium. The cell counting was carried out using the Goryaev chamber. The living yeast cell concentration (stimulation) was increased under exposure to low doses (10 cGy) of ionizing radiation with a dose rate of 10-3 Gy/h. The radiation-induced adaptation was observed, which manifested itself as increase of half-lethal doses at subsequent acute radiation exposure in the dose range of 2 to 12 kGy, for cells that were preliminary irradiated with an adapting dose of 10 cGy. The radioresistance changed when the time interval between adapting and acute radiation exposure was 5 hours and more. And the dose modification factor increased with the growth of this time interval. This result is explained by the available time necessary for biological response formation and development of radiation-induced adaptation.