A method to determine catechin in aqueous solution by measuring chemiluminescence intensities using a stopped flow system has been studied. The lucigenin-hydrogen peroxide chemiluminescence reaction was chosen for the determination of catechin. Fe(II) ion was added to the chemiluminescence system to increase the sensitivity. The chemiluminescence intensity from the lucigenin system was increased by the addition of catechin. Effects of flow rates of reagent and sample and concentrations of lucigenin, hydrogen peroxide, Fe(II) ion and KOH were investigated. The calibration curve for catechin was linear over the range from 1.0x10(-6) to 1.0x10(-3) M and the detection limit was 3.0x10(-7) M under the optimal experimental conditions.