Each of the metal nano-particles present in a dispersion, which comprises at least one metal selected from the group consisting of precious metals and transition metals or an alloy of at least two metals selected from the foregoing metals, comprises a metal particle in which an organic metal compound of a fatty acid and/or an amine-metal complex is adhered to the periphery of the metal particle. This organic metal compound and the amine-metal complex are admixed together in a solvent and then the resulting mixture is subjected to a reducing treatment to thus form a dispersion containing metal nano-particles in a concentration of not less than 5% by mass and not more than 90% by mass. The resulting dispersion is applied onto the surface of a base material, followed by drying the applied layer of the dispersion and then firing the dried layer of the dispersion at a low temperature to thus form a thin metallic wire or a metal film having conductivity.