The present paper is dealing with the bacteriological characteristics of phage-resistant strain which produces in culture of phytopathogenic Xanthomonas oryzae, the causal agent of rice plants. According to the literatures by many investigators, these phage-resistant strains (11/r, K7/r) isolated from their parent strains (11, K7) used in this experiment are considered to be the resulting products derived from spontaneous mutation. These phage-resistant strains are characterized by the loss of susceptibility against the phages OP_1 and OP_1h in vitro. Comparative studies on these strains revealed the facts that there are no apparent differences in the morphological and physiological characteristics between parent strains and their phage-resistant strains, while apparent differences are in response to phages and rice plants. Immunity of phage-resistant strains to phage infection appears to be a stable and permanent characteristic which does not change after successive culture on slant of potato dextrose agar and after successive inoculation to rice plants. These phage-resistant strains, however, show less virulence to rice plants than that of parent ones. These phage-resistant strains possess the ability to produce the new phages which differ from the known virulent phages OP_1, OP_1h, and OP_2. The new phages obtained from three-day culture of phage-resistant strains in potato semisynthetic liquid medium are considered to be temperate phages after the results that they show smaller plaque forms than those of the known phages, immunity of parent strains to temperate phages, and the stable characteristics even after the two-times serial colony isolations of parent strains. In conclusion, then, it appears that such phage-producing strains are the lysogenic strains.