The improved metal-in-gap magnetic head has a thin ferromagnetic metal film and a gap film superposed on an oxide substrate in that order and an intermediate film made of a nonmagnetic metal or a semiconductor is formed either in the space between the oxide substrate and the ferromagnetic film or between the ferromagnetic film and the gap film or in both spaces and then heat treated to provide such a profile that the element forming the intermediate film is of high concentration at the interface between the ferromagnetic film and the oxide substrate or the gap film whereas said element is of low concentration and distributed in a substantially uniform and continuous manner throughout the interior of the ferromagnetic film.The ferromagnetic film is formed preferably of an Fe--Al--Si (Sendust) alloy, an Fe--M--N alloy or an Fe--M--C alloy (M=Zr, Ta, Nb, Hf, etc.). The intermediate film which contributes corrosion resistance is made preferably of at least one of Cr, Al and Si, with its concentration being preferably from 50 at % to less than 100 at % at the interface between the ferromagnetic film and the oxide substrate or the gap film but from 0.5 at % to 10 at % within the ferromagnetic film. To insure that the element which forms the intermediate film is distributed uniformly and continuously within the ferromagnetic film, the intermediate film is preferably heat treated at 500.degree. to 700.degree. C. for a period of 5 to 120 min.