Abstract: The kinetics of the reduction of Pu ( VI) with humic acid is investigated. Based on the data obtained, probable mechanism of the reaction is proposed with the reaction of Pu( V ) and humic acid as the rate-determining step, and the rate equation is deduced as follows:In the range of pH 1. 6-3. 2where K =24±4(mol/l)-1.3·min-1at 20℃ , activation energy E = 45±2 kJ·mol-1 and in range of pH 4. 6-6. 1where K =0. 23±0. 05(mol/l)-0.40·min-1 at 20℃.