Magnetic method is one of a prospective candidate for nondestructive evaluation before crack initiation, because magnetic properties are very sensitive to microstructures of the materials, and therefore are sensitive to the mechanical properties. This paper introduces the relations between the magnetic properties and the mechanical properties, the microstructures of materials firstly, and explains several magnetic parameters for nondestructive evaluations: hysteresis, permeability, Barkhausen noise, etc. Then, the several results of parameter changes on cold rolled low carbon steel are introduced. As other cases, results when scanning a probe over deformed samples are described (these include the reviews of our past works). Finally, since microstructures have anisotropy as well as the magnetic properties for the deformed sample, the results in such cases are introduced. The potential of nondestructive evaluation using magnetism for mechanical properties and degradation of steels will be introduced.