Abstract: The algal isozymes of POD,CAT,SOD and COD in the control and Potamogeton malaianus-exposure treatment were investigated using PAGE method to study the influences of allelopathy from P.malaianus)on Scenedesmus obliquus.Comparing with the control,the algal isozymograms of POD in the treatment systems changed while the number of bands remained stable.The algal isozyme band numbers of SOD decreased but the band numbers of CAT increased significantly.These results indicated that S.obliquus resist the reactive oxygen species(ROS)hurt from allelopathy stress by adjusting the isozymograms and activities of antioxidant enzyme.The study also presented the influences on COD isozymograms,which showed in a sense the allelopathic hurts on biological oxidation of algae.