Abstract: A metal thin film-forming method which comprises the step of firing metal nanoparticles each comprising a particle consisting of at least one metal selected from Ag, Au, Ni, Pd, Rh, Ru, and Pt or an alloy comprising at least two of these metals and an organic substance adhered to the periphery thereof as a dispersant, under a gas atmosphere containing water and/or an organic acid to thus form a metal thin film. This metal thin film possesses a low resistance value.