According to the invention, an iron oxide is provided for ferrite having a Mn content of 0,1 to 0,3 % by weight and a P content of not more than 0,005 % by weight. Such an iron oxide can easily be produced by making an iron chloride solution, dephosphorizing the iron chloride solution by a simple process and oxidizing roasting the dephosphorized solution to provide the desired iron oxide. Although Mn is contained as an impurity the ferrite properties are not impaired thereby since attention is paid to the impurities of P which are at a low level. Accordingly, soft ferrite can be produced having excellent ferrite properties.