Abstract: A method for preparing the immuno-stimulating complexes(ISCOMs)with theβ-hemolysin(β-HemA) and Quil A was described,in which the β-hemolysin of Aeromonas hydrophila was extracted by ammonium sulphate gradient precipitation and pretreated with an acidic pH(2.5)to reveal hydrophobic regions,and then was mixed with the Quil A and other reagents.The ISCOMs was a cagelike Structure with a diameter of 30—40 nm by negative contrast electron microscopy.Several groups of eel were immunized with β-HemA-ISCOMs,β-HemA-CFA and same amount of β-hemolysin without adjuvant,respectively,and followed by challenge with a virlent bacterial strain TPS-30.The protecion rates of that were 100%,62.5%,and 50%,respectively.The result indicated that the eel immunized with β-HemA-ISCOMs were effectively protected against the challenge.