A method of producing a permanent magnet having an ultra-high coercive force and a large maximum energy product, comprising steps of heating an alloy at 900.degree. to 1,400.degree. C. for one minute to 100 hours so as to effect homogenizing solid solution treatment, which alloy consists of 33.5 to 47.5 atomic % of platinum and the remainder of iron with a small amount of impurities, quenching said alloy in water or in air at a rate of 30.degree. C./minute to 2,000.degree. C./second, applying plastic working of not less than 90% to the thus quenched alloy by drawing into wire or rolling, reheating the worked alloy at 400.degree. to 700.degree. C. for one minute to 300 hours, and cooling the reheated alloy.