A surface-modified iron-based oxide magnetic particle powder has good solid-liquid separation property in the production process, has good dispersibility in a coating material for forming a coating-type magnetic recording medium, has good orientation property, and has a small elution amount of a water-soluble alkali metal, and to provide a method for producing the surface-modified iron-based oxide magnetic particle powder. The surface-modified iron-based oxide magnetic particle powder can be obtained by neutralizing a solution containing dissolved therein a trivalent iron ion and an ion of the metal, by which the part of Fe sites is to be substituted, with an alkali aqueous solution, so as to provide a precursor, coating a silicon oxide on the precursor, heating the precursor to provide e-type iron-based oxide magnetic powder, and adhering a hydroxide or a hydrous oxide of one kind or two kinds of Al and Y thereto.