In order to elucidate the effects of x-ray radiation on enzyme system of bacteria, the author studied the effect of x-ray radiation on enzyme system of Sal 57 S which were irradiated such large dosis as 8,000r in comparison with the enzyme activity of untreated cells. And the following results were obtained. 1) The oxidation of glucose and pyruvate was inhibited to a large extent on the enzyme systm of the x-ray irradiated organisms. And from the findings of the studies on RQ., stoichiometry and action of inhibitors, it could not find any difference on the oxidation pathway from glucose to pyruvate, but on the further oxidation pathway of pyruvate. The inhibition on the further oxidation pathway of pyruvate brought about marked accumulation of acetate in the cells of Sal 57 S irradiated to x-ray. 2) As concerns to the oxidation of member of TCA cycle, an inhibition was found at the oxidation of α-ketoglutalate and also of succinate to a slight extent. 3) The inhibition on the oxidation of glucose, pyruvate and α-ketoglutalate could be removed by addition of cysteine. From the view of this fact, the inhibition was supposed to be occured in the enzyme system relating to -SH group. 4) The effect of x-ray irradiation on oxydative phosphorylation was studied by measuring P:O ratio and P(32) incorporation into Δ-7-p. The decrease of P:O ratio and P(32) incorporation was observed. This fact possibly implied that the irradiation of x-ray acted as an uncoupler on oxydative phosphorylation 5) There was not observed any changes on the nucleic acids system of bacteria just after the x-ray irradiation. However, amount of DNA showed a decrease by a succeeding incubation of the organism after x-ray irradiation. An inhibition to the incorporation of phosphorus into DNA fraction was also proved on the cells by isotopic study using P(32).