Using Sal 57 S as test organism, the author studied the effect of x-ray radiation on the morphology of bacteria by means of electron microscope. The dosis given to the microorganism was 2,000r or 8,000r. The following results were obtained. 1) The morphology of the cells was kept almost normal as just after the irradiation. 2) Prominiently elongated bacteria were found on succeeding cultures of 2, 3 and 5 hrs after the irradiation. 3) There were found some regions that had a low electron density on elongated cell. The distances between the regions were almost normal cell size or somewhat exceeded on its size. With the lapse of cultivation time the region became more distinctive and wider. 4) The bacterial cells cultured following after the irradiation were lost its homogeneousness in part and revealed granule-like structure in its interior and in the sever case the body of cell turned to be a exuviae form. 5) As was found on the cultured cells mentioned above, the identical facts was observed by the bacterial cells stocked in refrigerator for 2 days following after the irradiation.