Abstract: The kinetics of liquid-phase hydrogenation of maleic acid to succinic acid was studied over skeleton nickel catalyst in aqueous solution at different values of pH. The dependence of the substrate concentration and the amount of hydrogen absorbed on time were used to determine the reaction orders and rate constants. The effect of external and internal diffusion was evaluated and taken into account. Different reasons for the effect of pH on kinetic parameters are discussed for the reaction occurring in aqueous solutions. The values of the reaction orders found in the pH interval under investigation differed from one and changed in the range of 0.7-0.85 and 0.50-0.85. Activation energies of maleic acid, the hydrogenation reaction in aqueous solution of sodium hydroxide with pH 7.8 and 13.9 equal to 39 ± 2 and 62 ± 5 kJ mol-1, respectively. Thus maleic acid hydrogenation reaction on a skeleton nickel in aqueous solutions despite simple kinetic regularities of the reaction process represents a complex non-stationary process complicated by strong diffusion retarding while constructing a kinetic model of the process under study.