Abstract: The present invention relates to a slurry for use in metal chemical-mechanical polishing (CMP) and a preparation method thereof. More particularly, the invention relates to a slurry for use in metal CMP, in which iron ions or divalent or higher valent metal ions are physico-chemically adsorbed on colloidal silica particles in the form of particles by a reduction, hydrolysis, impregnation or precipitation method, as well as a preparation method thereof. The slurry useful for metal CMP prepared according to the present invention has a uniform particle size distribution, and shows increased efficiencies as an oxidation catalyst and polishing slurry chemically adsorbed with metal particles, as compared to the prior metal CMP slurry distributed with metal ions. Also, the inventive slurry has long-term storage stability, since it does not show coagulation and precipitation phenomena even after it is stored for more than one year without a dispersant or a dispersion stabilizer.