Though bacteria of the radiation-resistant Deinococcus radiodurans have a high resistance to the lethal and mutagenic effects of many DNA-damaging agents, the mechanisms involved in the response of these bacteria to oxidative stress are poorly understood. In this report, the superoxide dismutase (SOD) and catalase (CAT) activities produced by these bacteria were measured, and the change of SOD and CAT activities by 20 keV N+ beam exposure was examined. Their activities were increased by N+ beam exposure from 8x 1014 ions/cm2 to 6x1015 ions/cm2.The treatment of H2O2 and [ CHC13 +CH3 CH2OH ] and the measurement of absorption spectrum showed that the increase in SOD activity was resulted from inducible activities of MnSOD in D. radiodurans AS1.633 by N+ beam exposure . These results suggested that this bacteria possess inducible defense mechanisms against the deleterious effects of oxidization. Although bacteria of the radiation-resistant Deinococcus radiodurans have a high resistance to the lethal and mutagenic effects of many DNA-damaging agents, the mechanisms involved in the response of these bacteria to oxidative stress are poorly understood. In this report, the superoxide dismutase ( Their activities were increased by N + beam exposure from 8 × 1014 ions / cm2 to 6 × 1015 ions / cm2. The treatment of H2O2 and [CHC13 + CH3 CH2OH] and the measurement of absorption spectrum showed that the increase in SOD activity was resulted from inducible activities of MnSOD in D. radiodurans AS 1.633 by N + beam exposure. These results suggest that this bacteria possess inducible defense mechanisms against the deleterious effects of oxidization.