Supported Ni/gamma-Al2O3 catalysts were studied in the gas phase hydrodechlorination of substituted chlorobenzenes. The catalytic properties of the catalysts were shown to be determined by the metal nickel. A correlation between the rate of the gas phase hydrodechlorination of substituted chlorobenzene and donor-acceptor properties of substituents was established. The electron-donor substituents increase and the electron-acceptor ones decrease their reactivity. The correlation analysis of data treated via the Hammett equation shows that hydrodechlorination on Ni/gamma-Al2O3 catalysts is a reaction of electrophilic type.