A systematic study of the synthesis of C.I. Acid Blue 9 leuco compound in water is reported. The kinetic analysis of experimental data for the condensation reaction between 2-formylbenzenesulfonic acid sodium and N-ethyl-N-(3'-sulfonic acid benzyl) aniline obtained at four different temperatures ranging between 85 and 100 degrees C is discussed. It is shown that the reaction followed second-order rate kinetics. The overall rate constant (k) increased with the increase of temperature. On the basis of the value of k, activation energy (Ea) of the reaction was evaluated. Importantly, it is found that reactant concentration has great effect on the formation of C.I. Acid Blue 9 leuco compound, implying that it is not enough to improve the conversion of N-ethyl-N-(3'-sulfonic acid benzyl) aniline by only prolonging reaction time in the late period of the reaction. (C) 2017 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.