Steel plates are generally used as a member of structures and machines. But they often cause a serious vibration and noise trouble. Against these troubles, there is a way to use damping steel plates in the structure element as a effective measure. Yet about one of the kind of the damping steel plate, the ferromagnetic damping steel plate is not well clear of its effects. They say damping characteristics goes down when it is structured. In this paper, we are invest the damping characteristics of these To make clear these reasons, we investigated the damping characteristic of these constructed structures, using S.D.E. (specific damping energy) method. And we introduce a method to predict damp-ing performance of structure at a design stage.