Abstract: The present study evaluated the inhibitory effect of Bacillus cereus strain JAQ04 against several pathogenic bacteria for tilapia under in vitro conditions. B. cereus strain JAQ04 was tested against Vibrio alginolyticus, Aeromonas hydrophila and Pseudomonas putida in a cross streaking assay, where B. cereus showed a strong antagonistic effect against the three tested bacterial fish pathogens. In the following test, B. cereus strain JAQ04 at 103, 105 and 107 CFU mL-1 was then tested against V. alginolyticus at 103 CFU mL-1 for 6 days in co-culture assay. The results revealed that higher concentrations (105 and 107 CFU mL-1) of B. cereus strain JAQ04 had higher inhibitory effect against pathogenic V. alginolyticus. Bacillus cereus strain JAQ04 was administered to juvenile tilapia to determine its safety for tilapia. The results showed that the Relative Percent Survival (RPS, %) was 70.83+18.2 which was not significantly different from the RPS of fish in the control group (78.50+3.5%).