A thin-film magnetic head having a magnetic core of double step structure and a method of fabricating it. A first magnetic core is formed on a substrate, which has a predetermined thickness at a pole chip region thereof and a thickness larger than the predetermined thickness at a back region thereof; a magnetic gap is formed thereon, a conductor coil is formed on the magnetic gap, which is encircled by an inter-layer, insulating film; a first magnetic film is formed thereon, which constitutes one layer of a second magnetic core and is connected with the first magnetic core at the back region; and a second magnetic film is formed thereon through an inorganic insulating film, which constitutes another layer of the second magnetic core and is removed at the pole chip region. When the second magnetic film is removed, the inorganic insulating film serves to protect the first magnetic film, and hence the thickness of the first magnetic film is maintained unvaried. Thus, there is obtained the thin-film magnetic head having a magnetic film which is of a predetermined thickness at the pole chip region and a thickness larger than the predetermined thickness at the back region.This structure enhances the conversion efficiency of the head as well as boosts the resolution for reproduction and relaxes the magnetization saturation for recording.