Abstract: To investigate the abscisic acid(ABA) production, soluble protein level and water potential of water hyacinth Eichhornia crassipes (Mart. Solms) leaves in response to diurnal low temperature stress, plants with 12 pieces of leaves were exposed to constant temperatures of 2, 4 and 8℃ for 72 hours and leaves were sampled at 0, 4, 24, 48 and 72 hours. ABA quantities were measured by using HPLC techniques. Lowry method was used to measure soluble and capillary method was used to measure water potential. Various low temperatures significantly increased ABA and soluble protein levels compariscd with control temperature (24—26℃), ABA and soluble protein increased with temperature decreasing. Cycloheximide was found to inhibit protein synthesis in the leaves at 2℃ more than at 24—26℃. Since normal water potentials were obtained in plants of all temperatures, the observed ABA response was not due to temperature-induced water stress. Temperature stress induced the plant to produce high level of ABA.