Six strains of radiation-resistant gram-positive cocci were isolated from sewage sludges and animal feeds in Japan after gamma-irradiation of more than 1.0 Mrad. All six strains were able to grow on nutrient agar slants, and some strains were also able to grow on glutamate agar slants. Cells of the six strains were single or diplococci, and occasionally seen in tetrads, being spheres averaging from 0.8 to 1.0 μm in diameter. The peptide subunit of cells of all the strains contained ornithine, and the predominant fatty acid component was a C16:1. The GC content of the DNA of these strains ranged from 59 to 66 mol% thus indicating them as belonging to the genus Deinococcus Brooks and Murray 1981 which was previously called the “Micrococcus radiodurans” group. From the similar cultural characteristics and morphology, the six strains, TD1, TD3, TD9, T843, Fr 3 and Fr 7, were identified as D. proteolyticus. However, the predominant component of cellular fatty acids of strain T843 was similar to that of D. radiodurans. The resistance to gamma-radiation of these new isolates was similar to that of D. radiodurans R1 and D10 values in phosphate buffer ranged from 0.10 to 0.25 Mrad, and the low oxygen enhancement effect caused by radiation was distinct from other kinds of bacteria.