A new kinetic method has been developed for the measurement of Mn(II) in water samples. The method is based on the catalytic effect of Mn(II) with the oxidation of Celestine blue (CB+) by KIO4 using 1,10-phenantroline (Phen) as an activator. The optimum conditions obtained are pH 4.5, 0.1 M acetate buffer solution, 4.0 x 10(-4) M KIO4, 4.5 x 10(-5) M CB+, 1.0 x 10(-4) M Phen, reaction temperature 40 C and reaction time of 4.0 min at 640 nm. Under the optimized conditions, the method allowed the measurement of Mn(II) in a range of 0.1-5.0 mu g L-1 with a detection limit of 0.023 mu g L-1. The recoveries in measuring the standard Mn(II) solutions of 0.5, 2.0 and 4.0 mu g L-1 were in the range of 97-103%, and the relative standard deviations (RSDs) were in a range of 3.0-0.8%. The method was applied satisfactorily to the determination of Mn(II) in some environmental water samples. The reliability of method was also verified by determining the manganese content of the certified standard reference river water sample, JAC-0031. Compared with the previously published catalytic-kinetic methods and instrumental methods, the method showed fairly good selectivity and sensitivity, low cost, cheapness, low detection limit and rapidity. It can easily and successfully be applied to the natural water samples.