Preparation and utilization of nano-sized metal particles are of interest in a variety of fields including electronics, optics, catalysts and colorants. In order to utilize the nano-sized particles industrially, mass production of stable and highly concentrated dispersion is necessary. We have developed a novel method to produce such dispersions of nano-sized metal particles having 2 – 50 nm diameter. The method consists of colloidal stabilization by specially designed block copolymer and reduction of metal ions under presence of alkanol amine.Up to now we have succeeded to prepare the colloidal pastes of Ag, Au, Pt, Pd, Ni, Bi and Au/Ag alloy with metal concentrations of more than 30% in a variety of solvents such as water, alcohols, esters, ketones and aromatic hydrocarbons.These colloidal pastes are applicable to Ink Jet Printing owing to their excellent stability and nano-sized diameter. Printed patterns exhibits metal like appearance, electroconductivity, clear red and yellow colors and catalytic activity depending on species and concentration of the metal.