Abstract: By measuring the CAT activities of aquatic plants exposed to heavy metals of Pb and Zn, the experimental results show that the order for the CAT sensitivities of three plant species is: Alternanthera philoxeroides> Spirodela polyrrhiza > Potamogeton malaianus. It is contrary to the results of ecological sensitivities showed by three plant species with tissue injured, such as: Potamogeton malaianus > ,Spirodela polyrrhiza > Alternanthera philoxeroides. It is said that the signification about ecological sensitivity is different between both ecological levels of organizm and molecule.