The effect of magnetic yoke properties on the results of the magnetic NDE using impedance measurement was investigated. The measurement impedance depends on the yoke materials, thus, an estimation of initial permeability of specimen evaluated from the obtained impedance profile is required, because the initial permeability of the specimen has good correlation with mechanical properties and microstructures. We can calculate the impedance profile on the basis of equivalent magnetic circuit analysis, and therefore, we can estimate an initial permeability of specimens from the experimental results with comparing calculation with experimental results.