Solid sols of rhodium, palladium, platinum, silver, and gold in poly(methyl methacrylate) (PMMA) were prepared by the solidification (polymerization) of solutions of starting noble metal compounds in methyl methacrylate monomer and postheating of the resulting solid solutions of the compounds in PMMA. The solid sols were found to contain ultrafine particles of noble metals and have characteristic colors due to the particles. The formation of the noble metal particles in PMMA during the course of postheating was investigated by their absorption spectra.