The study was conducted to screen the antibacterial activity of fermented garlic against V. parahaemolyticus KC.13.14.2 and V. harveyi KC.13.17.5, the causal agent of acute hepatopancreatic necrosis disease (AHPND). The results showed that fermented garlic products had a high sensitivity to both strains of screened bacteria at concentrations of 25 and 30 μl. Then the effect of fermented garlic as an agent for the prevention of AHPND was evaluated in vivo. When adding fermented garlic at a dose of 15 ml/kg food/day to feed shrimp for 10 consecutive days, it was possible to prevent AHPND disease for shrimp. Food mixed with fermented garlic with squid oil was the most effective when it increased the survival rate of shrimp to 53%, significantly higher than treatment using supplementary feed without a coating of 51%, coated with glutinous rice of 42%, and no fermented garlic of 14%.