This paper presents the perpendicular magnetic properties and microscopic structures of Co-ferrite films prepared by a heat-oxidation process of evaporated Fe-Co multi-layered thin films. The oxi-dation temperature is less than 550°C. Thin films are oxidized in 760 Torr O₂ atmosphere under a magnetic field of 1 kG applied in the perpendicular direction to the film surface. Co-ferrite films are evaluated using as follows: (a) the crystal structure is analyzed using an X-ray diffractometer, (b) a SEM is used in observations of surfaces and cross-sections, (c) composition distributions in the film depth direction are investigated by AES and XPS, (d) a VSM is used to measure hysteresis loops, and (e) a magneto-optical property is measured from Kerr-rotation angle. One cause of the perpendicular magnetic anisotropy of the oxide films is thought to be the effect of the columnar grain growth of oxide particles which facilitated by growing vertically along grain boundaries.