Several metal colloids stabilized by an amphiphilic copolymer, poly(1-vinylpyrrolidone-co-acrylic acid) (abbreviated as PVPAA), were prepared by refluxing alcohol-water mixed solutions of the corresponding metal precursors. They had small particle sizes and narrow size distributions. Their catalytic activity was tested by hydrogenation of cyclooctene, 1-dodecene, and ortho-chloronitrobenzene (o-CNB), With the introduction of nickel(II) ions to a PVPAA-stabilized platinum catalytic system, selective hydrogenation of o-CNB to ortho-chloroaniline (o-CAN) with 97.1% selectivity and 100% conversion was obtained.