A great variety of monosubstituted nitrobenzene derivatives has been reduced in good yield to the corresponding anilines with hydrazine hydrate in the presence of an iron oxide hydroxide catalyst prepared by precipitation from an aqueous iron(III) solution with sodium hydroxide. The dependence of the rate of reduction on the nature and the position of additional substituents other than the nitro group was determined by measuring the reaction kinetics. The rate is enhanced by electron-attracting substituents and decreased by electron-donating groups, which results in a positive slope of rho=0.546 for the Hammett plot. Competitive reduction experiments with mixtures of two differently substituted nitrobenzene derivatives revealed that the nitro compound with the more electron-attracting substituent is reduced first.