In last 30-35 years, it has been discovered that many organisms can live in environments considered as extreme for mankind. Since these microorganisms can live in the extreme environments, they are named as extremophiles. One of the discovered microorganisms, Deinococcus radiodurans, had drawn attention for its extraordinary capabilities and its potential of infinity. D. radiodurans is resistant to genotoxic chemicals, oxidative damage, high-level ionization, ultraviolet radiation and dehydration. Because of these features one can name it polyextremophilic. In recent years, studies on bioremediation and related to heavy metal and detoxification of xenobiotics which cause serious environment problems, as well as genetic engineering, have been intense. However, the reactive oxygen species, induced by UV and their effects, their cellular defense mechanisms against ROS and about antioxidative systems responsible for cleaning of reactive oxygen species enough research has not been made.To this end; in Ecsherichia coli and radiation-resistant D. radiodurans bacteria were compared and tested effects on levels reduced glutathione (GSH) and antioxidant system of radiation. In both bacteria, enzyme activity and GSH levels has been determined after the different doses of gamma radiation applications. In the end of our study, high activities in enzyme especially superoxide dismutase and catalase of D. radiodurans were observed depending on the different doses gamma radiation applications. We were also observed that GSH quantity and other enzymes had a low activity in the cell. Moreover, it was determined that enzyme and GSH levels were decreased in E. coli depending on the radiation levels.