Abstract: This study aimed to characterize Bacillus sp. NP5 and to evaluate the effectiveness of its application as a probiotic on growth performances and health status of common carp (Cyprinus carpio ) before and after infected by Aeromonas hydrophila . Bacillus sp. NP5 cells were given to common carps through the feed for 30 days at doses of 106, 108 and 1010 CFU g–1 feed. On day 31, common carps were challenged with A. hydrophila , which was injected via intramuscular route. Result of phenotypic and genotypic identification of Bacillus sp. NP5 isolate showed that this isolate was Bacillus cereus with 99% of similarity index. Bacillus sp. NP5 was able to produce protease, amylase and lipase, it was also potential to inhibit A. hydrophila, Streptococcus agalactiae and Mycobacterium fortuitum. Supplementation of feed containing probiotic at a dose of 1010 CFU g–1 feed resulted a higher total bacterial count and a higher total probiotic count in the intestine, those followed with higher value of amylase, protease and lipase activity, along with the highest daily growth rate and the lowest feed conversion ratio (p<0.05). Total leukocytes and phagocytic activity in probiotic treatment with a dose of 1010 CFU g–1 feed was higher (p<0.05) compared to controls at the end of the rearing period over 30 days. Common carps fed probiotic showed survival rates after the challenge test with values ranging between 81-100%, while the survival rate of fish without probiotic supplementation was only 50%. The results of this study showed that probiotic supplementation on common carp could reduce the pathogenicity of disease caused by A. hydrophila infection, which indicated an improvement in cellular immune response.