The aim of the study was to assess the effect of metformin (an anti-hyperglycemic drug in type 2 diabetes (T2D) patient) on DNA oxidative damage in vitro in human peripheral blood lymphocyte from 10 donors; evaluation of the oxidative damage induced by 1 and 2 Gy gamma rays; and assessed the role of metformin in protecting lymphocytes against the oxidative damage induced by gamma rays. The 8-Hydroxydeoxyguanosine (8-OHdG) ELISA Kit was used to detect the DNA oxidative damage in blood lymphocytes. Metformin (10 and 50µM) in vitro increased the rate of (8-OHdG) significantly (P ≤ 0.001) than control samples value. Irradiated blood lymphocyte with 1 Gy gamma rays elevated the DNA oxidative damage in rate (95%) and significantly (P ≤ 0.001) than control values, and the rise of irradiation into 2 Gy, caused increase the DNA oxidative damage (8-OHdG) 2.3 folds and significantly (P ≤ 0.001) than 1 Gy irradiated. Blood treated with metformin prior irradiation enhance the reduction of (8-OHdG) specially in blood irradiated by 2 Gy gamma ray, the reduction significantly (P ≤ 0.05 and P ≤ 0.001) respectively for (10 and 50 µM) metformin treated compared with irradiated group only.