Colloidal dispersions of polymer-protected Cu/Pt alloy dusters have been prepared for the first time by reduction of the corresponding metal hydroxide with a cold alloying process. The Cu/Pt (mole ratio = 1/1) colloid with an average diameter of 19 Angstrom and Cu/Pt (3/1) with an average diameter of 23 Angstrom have the alloy structure of CuPt and Cu3Pt, respectively. Colloidal dispersions of polymer-protected Cu/Pd bimetallic alloy clusters have also been prepared by the same method at various Cu/Pd ratios. These bimetallic clusters exhibit excellent properties as the active and selective catalyst for the hydration of acrylonitrile to acrylamide as well as the hydrogenation of 1,3-cyclooctadiene to cyclooctene.