Abstract: The invention aims to provide a rare earth metal-based permanent magnet which has on the surface an inexpensive corrosion-resistant film combining excellent heat-resistance with excellent adhesiveness; a process for producing the permanent magnet; and a treating liquid for forming the corrosion-resistant film. The invention provides a rare earth metal-based permanent magnet characterized by it has on the surface a corrosion-resistant film containing lithium silicate and a thermoplastic resin as the constituting components, the film containing uniformly dispersed therein the thermoplastic resin at a content of 0.1 wt % to 50 wt %. The treating liquid, which is an excellent liquid for forming the corrosion-resistant film, is characterized by that a soap-free aqueous emulsion of a thermoplastic resin was used and that it contains the thermoplastic resin and lithium silicate in given amounts.