Abstract: This paper reported the fulminant haemorrhagic disease of hybrid Tilapia(O. niloticus×O. aureus) in Hainan, China. The typical symptoms of the disease include: Congestion and hemorrhage in skin, muscle, liver and fins; decay in the end of dorsal and caudal fins;enlargement in gallbladder. Five kinds of bacteria were isolated from the sick tilapia with typical syndrome and one of them was proved to be its pathogen by artificial challenge. The pathogen was identified as Aeromonas hydrophila by morphological observation and biochemical test. The LD₅₀ of the pathogen to healthy tilapia was 1.14×10⁴ cfu · g^-1 by intraperitoneal injection challenge. The antibiotic sensitivity analysis showed that Tobramycin, Gentamycin, Amikacin, Chloramphenicol, Kanamycin, Rifampicin, Furazolidone and Nitrofurantoin are sensitive to the pathogen and could be selected as its curing medicine.