Disclosed is a method of forming a ferrite film on particulate and/or fibrous substrate by adding an oxidizer solution and a ferrous ion solution to a deoxidized solution containing particulate and/or fibrous substrates to form a thin ferrite film on the particulate and/or fibrous substrates, wherein an addition amount of the ferrous ion solution is controlled such that an oxidation-reduction potential of the deoxidized solution keeps approximately a center point between the oxidation side and the reduction side, when a pH value of the dioxidized solution is adjusted to a constant value between pH 6 and 10.