JPH0551538B

Magnetic iron oxide containing silicon element is produced in the form of generally octahedral particles having a sharp particle size distribution through a reaction of an aqueous solution of a ferrous salt having a controlled Fe(II)/Fe(III) ratio and containing a silicic compound with a little excess of an alkali, followed by oxidation of the resultant ferrous hydroxide. The magnetic iron oxide particles have an overall content of silicon element of 0.1-1.5 wt. % based on the iron element with the silicon localized at the core of the particles. The magnetic iron oxide particles have uniform surface properties not markedly changed under various conditions and have good dispersibility in a resin.