We investigated magnetic properties of representative soft magnetic materials, then clarified that non-oriented iron-silicon steel maintains high permeability and shows the most stable temperature dependence of the properties in the temperature range from room temperature to 600°C. The fundamental element for the development of a magnetic field sensor using non-oriented Fe-Si steel was composed and the changes in inductance of the element, are proportional to the permeability of the material, were evaluated by applying a magnetic field to the element. The inductance decreases with increasing the magnetic field almost linearly, indicating the possibility of a magnetic field sensor operating at high temperature up to 600°C.