Grain size dependence of magnetic properties is measured for mild steel specimens. The grain size, which as wel as the chemical composition affects the mechanical properties of steel, is required to be evaluated nondestructively in the manufacturing process. The magnetic properties, such as permeability, also depend on the grain size. This dependence can be used for nondestructive evaluation of the grain size. In this study, the permeability, coercivity, residual magnetization, hysteresis loss, and anhysteretic permeability are measured for the steel specimens with various grain size. We found that the permeability, coercivity and the hysteresis loss depend on the grain size, while the residual magnetization is almost independent. This can be attributed to the measurement using the probe with permalloy core, since the saturation magnetization is about one third of that of the steel.