A research on the kinetics of nitrate removal has been made in the system composed of iron nanoparticles and Alcaligenes eutrophus, which is a kind of hydrogenotrophic bacteria. The experiment results showed that the nitrate removal in this integrated system could be expressed by two sequential first order expressions. However, when the amount of iron nanoparticles was greater than 0.56 g.L-1 or the optical density of the bacteria at 422 nm was less than 0.0009, the two sequential first order expressions may just be merged into one first order expression. In addition, the kinetic competition between iron nanoparticles and bacteria has been verified in this study. In the first few days of the denitrification process, the first order reaction rate constant (k(obs)) increased with the decrease of the initial concentration of the bacteria and the increase of the initial amount of iron nanoparticles. Moreover, a decrease in the initial nitrate concentration from 80 mg.L-1 to 20 mg.L-1 led to a 4-fold increase of the removal kinetics in both the first and the second kinetic expressions. (C) 2009 Elsevier B.V. All rights reserved.