Goldfish were fed with diets containing 0.02%and 0.002% of Furpyridinol(P-7138)for 120days. Compared with the control group, the medicated groups did not show any unfavourable effects on survival rate, weight gain, behavior, etc. During the experiments the infection with chondrococcus occurred in the control group. However, no infection was observed in the medicated groups. These results suggested that the oral administration of this drug, which showed high antibacterial activity in vitro against chondrococci(MIC:0.003-0.01mcg/ml), might prevent the infection with chondrococci in goldfish.