A magnetic thin film manufacturing method in which an object of treatment is electroplated in a plating bath so that a magnetic thin film is formed on the surface of the object of treatment. The plating bath contains two or more types of ions selected from a set consisting of Fe.sup.2+ ions, Ni.sup.2+ ions and Co.sup.2+ ions, and fine particles of an insulating material are dispersed in the plating bath. In a more particular embodiment of the invention, a magnetic thin film manufacturing method is characterized by the fact that �a! the aforementioned two or more types of ions selected from a set consisting of Fe.sup.2+ ions, Ni.sup.2+ ions and Co.sup.2+ ions are supplied by means of sulfates and/or chlorides, �b! the plating bath is an acidic bath, and �c! the fine particles of an insulating material that are dispersed in the plating bath are colloidal particles of SiO.sub.2 and/or Al.sub.2 O.sub.3.