This invention concerns a heat treatment method for rare earth type permanent magnets which are primarily of the Nd-Fe-B type. With regard to these permanent magnets, which oxidize rather easily in the air, the alloy is crushed, and either compression formed in a magnetic a non-magnetic field, sintered at 900.degree. to 1,200.degree. C., and then machined into the shape desired, and then solution treated in an atmosphere of oxygen and/or nitrogen at a temperature of 900.degree. to 1,200.degree. C., and then aged at 300.degree. to 900.degree. C. in order that an oxide and/or nitride protective layer of 0.001 to 10 .mu. be formed on the surface of the permanent magnet to prevent corrosion and in order to relieve machining strain.