Recently the metallic magnetic powders have been recognized to be better materials for high density magnetic recording. Superior quality magnetic tapes have been made with these metallic powders. But there are some problems remined they are easily corrodible and are rather difficult to disperse in the lacquer. To study the causes of chemical instability of these materials and to prevent their corrosion are very important for their applications in practice. The causes of chemical instability of metallic powders are studied by M?ssbauer effect and other experimental methods. Their corrosion may be prevented basically. This study will provide some useful data for their practical applications.