Abstract: The leaf area index, chlorophyll content,photosynthetic intensity and solublesugar content in leaves of Eichhornia,crassipes were higher than those in Alternan-thera philoxeroides at normal temperature(25℃-30℃).When the plants wereexposed to chilling temperature(2℃)for 12-48 hours,a decline was observed inthe activity of peroxidase,catalase,amylase and cytochrome oxidase in both E. crassipet and A. philo xeroides.Changes of enzyme activities were greater in the former plant than those in the latter.There were negative correlations between theenzyme activities,or the root vigor and the duration of low temperature. The experimental results suggested that E. crassipes was less resistant to chilling than A. philoxerotdes.