Aeromonas hydrophila causes a disease that often infects fish and is known as Motile Aeromonas Septicaemia (MAS), Hemorrhagi Septisemia, Ulcer disease or Red-Sore disease. The aims of this study were to develop polyclonal antibody of Aeromonas hydrophila in the rabbits to confirm the diagnosis of Aeromonas hydrophila in the fish by immunohistochemistry staining method. Preparation of polyclonal antibodies was performed on the rabbits used to Aeromonas hydrophila bacteria that have been tested biochemically by intravenous and intraperitoneal injection. Doses of Aeromonas hydrophila bacteria were 109 CPU/ml of 0.5 ml at first injection, 1 ml at second injection, 2 ml at thirth injection and 3 ml at fourth injection. Blood serum collection was performed at week 5 after injection from an ear and intracardial vein. The result of antibody titer was 28 = 1024 which measured by tube test. Furthermore, polyclonal antibody was used to immunohistochemistry staining with 400x dilution. The results of the staining showed that an immunopositive reaction in the liver, skin,lien, gill, kidney, and heart of fish to Aeromonas hydrophila antibody. The research conclution was polyclonal antibody from rabbit can be used to accurately confirm the diagnosis of Aeromonas hydrophila based on antigen and antibody reaction.