The eddy current loss at low frequencies in thin strips of isoperm under superposed magnetization by alternating and direct currents has been analyzed with a model of coherent rotation in magnetic domains. It is considered that the eddy current loss anomaly is not only caused by the displacement of the domain walls, but also by the rotation of magnetization. As the magnetic permeability is a tensor in the rotation process, it gives rise to a "laterat eddy current" term in addition to that given by the classical theory. Thence an expression has been derived for the anomaly coefficient ηr of the eddy current loss due to rotation. The theory has been extended to certain applied fields, and corresponding conclusions have been obtained.