Background: Irradiation leads to increased storage lesions that may have harmful effects if transfused. Various storage lesions research has been carried out, and only very few articles are available on the impact of gamma irradiation on RBC storage lesions. Since there has been no study about finding the best time for irradiation, we decided to investigate the effect of irradiation on Red blood cells at different storage times after blood collection Materials and Methods: A total of 40 units of Red blood cells divided into two groups, irradiated and nonirradiated. Irradiated RBCs were divided into three groups and each group containing ten units. The remaining ten units were consideRed as non-irradiated controls. Sampling from these irradiated and non-irradiated blood units was performed weekly to evaluate biochemical parameters and free plasma hemoglobin/Hemolysis index levels. Results: A significant increase in the mean values of plasma potassium, plasma Hb/Hemolysis index, and LDH, as well as a significant Reduction in the mean value of 2, 3 DPG and plasma sodium, were observed in both groups. Although the Reduction of 2, 3 DPG is extremely remarkable, it is compensated 24-48 hours after transfusion. Hence, the clinical result of 2, 3-DPG-depleted RBC transfusion is known to be negligible. The irradiation group alteration was more notable than the non-irradiated one and the changes in the parameters were most significant in the group having been stoRed for a longer period after irradiation. Conclusion: Our investigation on the impact of gamma irradiation on RBCs makes it possible to suggest a storage time up to 28 days after irradiation is permissible and the best time for irradiation after blood collection is up to 14 days. It is pointed out that the blood unit should be transfused as soon as possible after the irradiation.