Abstract: The present invention is a metal colloid solution comprising: colloidal particles consisting of metal particles consisting of one or two or more metal(s) and a protective agent bonding to the metal particles; and a solvent as a dispersion medium of the colloidal particles, wherein: a chloride ion concentration per a metal concentration of 1 mass % is 25 ppm or less; and a nitrate ion concentration per a metal concentration of 1 mass % is 7500 ppm or less. In the present invention, adsorption performance can be improved with adjustment of the amount of the protective agent of the colloidal particles. It is preferable to bind the protective agent of 0.2 to 2.5 times the mass of the metal particles.