A nano-metal solution, nano-metal complex grains, and a manufacturing method of a metal film are provided. The nano-metal solution includes metal grains having an amount of 0.1˜30 wt %, metallic-organic self-decomposition molecules having an amount of 0.1˜50 wt % and having formula 1, and a solvent having an amount of 20˜99.8 wt %: wherein M represents a metal ion. The metallic-organic self-decomposition molecules and the metal grains are evenly mixed in the solvent, and the metallic-organic self-decomposition molecules are adsorbed on surfaces of the metal grains.