Abstract: In an acetate buffer medium of pH 4.7,the oxidative color-fading of brilliant cresol blue by its reaction with hydrogen peroxide was catalyzed by Cr3+,Co2+ or Fe3+ and also the mixture of the 3 cations,leading to enhancement of color fading.But no additivity among the analytical signals of the 3 cations was found,possibly due to differences in speed of the catalytic reactions with the 3 cations individually.Artificial neural network (ANN) was applied to the treatment of such non-linear data,and based on which a method for simultaneous determination of Cr3+,Co2+ and Fe3+ in their mixtures by catalytic kinetic spectrophotometry was proposed.Six mixtures of the 3 cations with different concentrations were analyzed by the proposed mehtod,giving relative errors among the analytical results in the range -4.6% to 4.9%.