Iron powder ( and other metal powders) is widely used as a reactive barrier for removal of some contaminants, in particular aromatic nitro compounds and aliphatic chlorine derivatives from groundwater samples. Reduction of nitrobenzene, as a representative of nitroaromatic compounds with the iron material, was used as a test reaction to evaluate the surface reactivity of iron particles. This reaction exhibits pseudo first-order kinetics. The relationship between kinetic parameters and surface area as well as the influence of iron surface state on the reaction kinetics was investigated. Freshly chemically activated powders were always found to result in a faster process than other methods of pretreatment. It was also observed that with increasing particle size, i.e., with a decrease in specific surface of the powder, the reaction rate decreases.