The pretreatment solution for electroless plating of the present invention is composed of noble metal colloidal nanoparticles, a sugar alcohol, and water. The colloidal nanoparticles are gold, platinum, or palladium, have an average particle diameter of 5 to 80 nm, and are contained in the pretreatment solution in an amount of 0.01 to 10 g/L as metal mass. The sugar alcohol is at least one selected from the group consisting of tritol, tetritol, pentitol, hexitol, heptitol, octitol, inositol, quercitol, or pentaerythritol and is contained in the pretreatment solution in an amount of 0.01 to 200 g/L in total. The electroless plating method of the present invention uses the pretreatment solution and performs the electroless plating in an electroless plating bath.