Hydrogenation of o-chloronitrobenzene has been studied in methanol at 303 K and atmospheric pressure over polyvinylpyrrolidone-stabilized platinum colloidal clusters. The catalytic properties of platinum clusters for the hydrogenation of o-chloronitrobenzene to o-chloroaniline were remarkably affected by the metallic cations added. Among these cations, the most favorable influence on activity and selectivity was obtained when Ni2+ ions were used as modifier. The selectivity for o-chloroaniline was increased from 44.7% without a modifier to 66.3% when Ni2+ ions were introduced into the catalyst system, while the activity of the catalyst was nearly doubled by the addition of Ni2+ ion (the average rate of hydrogenation increased from 0.34 mol H-2/mol Pt s on neat platinum cluster to 0.64 mol H-2/mol Pt s on the Pt-Ni2+ system). The highest activity (0.72 mol H-2/mol Pt s) and selectivity (82.9%) to o-chloroaniline was obtained when the molar ratio of Ni2+/Pt was 8.