PURPOSE: To obtain ferromagnetic metal powder having excellent magnetic characteristics and oxidational stability by a method wherein the crystallite size of the maghemite present in an oxide film is specifically prescribed.

CONSTITUTION: The crystallite size Dγ of the maghemite present in an oxide film is 0.7 to 1.2 time of the thickness Dox of the oxide film. In order to form the crystallite of the maghemite in the surface oxide film in the size Dγ of the above-mentioned range, a low-temperature plasma treatment of ferromagnetic metal powder after it has been compounded, and also a method in which the powder is brought into contact with ozon-containing gas are considered effective. The thickness Dox of the surface oxide film of the metal particles, with which the ferromagnetic metal powder is constituted, is 20 to 45, desirably 25 to 40.