PURPOSE: To form a protective film having excellent wear resistance by coating a silicic acid soln. contg. a hardener or said soln. incorporated therein with a water-soluble resin on a thin magnetic metallic film provided on a non-magnetic substrate then heating the entire part in a specific temp. range.

CONSTITUTION: An aq. soln. prepd. by adding a suitable amt. of a hardener such as hydrochloric acid, phosphoric acid, aluminum chloride, acetic acid or the like to a soln. of silicate of an alkali metal such as potassium silicate or the soln. prepd. by adding ≤20wt% a water-soluble resin such as PVA, polyacrylic acid or the like according to need to said aq. soln. is coated on the thin magnetic metallic film of a magnetic recording medium to be used for a magnetic disc, magnetic drum, etc. The entire part is heated at 40W300°C after the coating and is dehydrated and cured. The magnetic recording medium of a long life formed with the protective film having excellent wear resistance and smoothness without giving any adverse influence on the magnetic characteristic is thus obtd.