Abstract:[Objective] The efficacy of the CP7 antimicrobial proteins (CP7ACP) to Aeromonas hydrophila was evaluated to provide potential novel natural drug for treating fish disease caused by Aeromonas hydrophila. [Methods] The effect on Growth, phosphorus divulges and biomacromolecule of Aeromonas hydrophila S12 were tested using Antibacterial test, Mo-Sb colorimetry and UV spectroscopy, while destructive effects of Aeromonas hydrophila cell structure by CP7ACP were observed under both scanning electron microscope and transmission electron microscope. [Results] The inhibition zone diameter was about 8.1 mm, the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) was 1/8 and 1/4 of stock solution respectively. After treated by CP7ACP, electron microscope reveals that cell wall, membrane, organelles and the thallus of Aeromonas hydrophila are subject to different degrees of damage, while intracellular biomacromolecule and phosphorus significantly divulge, genomic DNA become hyperchromic effect. [Conclusion] CP7ACP inhibit the growth of Aeromonas hydrophila, can be used for preventing fish disease caused by Aeromonas hydrophila.