1.Xanthomonas oryzae bacteriophage (OF_1 phage) intruded into X. oryze No.49 at 30℃ in vitamin free casein hydrolysate medium, multiplied with the average burst size of 7, and with the rise period of 20min. 2. The addition of 0.0045 M of CaCl_2 to the vitamin free casein hydrolysate medium increased the burst size up to12, with no effect both on the latent period and rise period. 3. Within the press-juice of rice leaves, the phage could not multiply and was inactivated gradually. 4. The temperature seems to affect the latent period and probably the burst size of OP_1 phage. In this experiment the optimum temperature for the growth of OP_1 phage seems to be about 30℃. At 20℃ the latent period was prolonged to abbut 80 min., but when the host-phage complex was kept at 30℃ for the initial 10 min. just after infection and then placed at 20cc, the normal latent period of 40min. was unchanged. In the experiment when the host-phage complex was incubated at 30℃ for the initial 10 min. Just after infection and then was placed at 10℃, the complex remained at a dormant state. When the latter was again replaced at 30℃, the phage multiplication was continued. At 40℃, the host-phage complex was in activated rapidly.