This study focused on the isolation, characterization, and screening of bacterial isolates from Sargassum oligocystum Montagne against Vibrio harveyi. The most effective isolate was identified and inoculated in commercial fish feeds as a probiotic supplement.Six bacterial isolates were isolated from the seaweed sample and screened against Vibrio harveyi. Two of the most effective among the six isolates were chosen and further screened against Vibrio harveyi. Bacterial isolate 1 identified as Bacillus cereus complex was incorporated in commercial fish feeds with and without seaweeds. Results showed that B. cereus complex with S. oligocystum had a viability of 12 days. The final population count was also higher in Bacillus cereus complex with S. oligocystum (M=9.83 log CFU/g) showing a significant difference in the treatment with B. cereus complex only. Thus, B. cereus complex grows better in fish feed supplemented with powdered S. oligocystum.