Abstract Aeromonas hydrophila bacteria that cause MAS (Motile Aeromonas Septicemia) disease. Cinnamon contain essential oils, tannins, saponins, flavonoids and phenols. The active compounds of cinnamon essential oil were cinnamaldehyde and cinnamic acid that can inhibit the growth of bacteria. The research was carried out from March to July 2022 at the Laboratory of Fish Parasites and Diseases…