To study the mechanism of the susceptibility changes of cupro-zinc superoxide dismutase(SOD)to proteases induced by reactive oxygen species is the aim of this work. By hydrophobic chromatography,hydrophilic and hydrophobic form of SOD was isolated from SOD modified by hydrogen peroxide or ascorbate-Fe(Ⅲ)system.The hydrophobic form of SOD demonstrated a high proteolytic susceptibility to trypsin and pepsin than both the native and hydrophilic form of SOD.The results suggested that the increased hydrophobicity of SOD might be responsible for its high susceptibility to proteases.