A method of manufacturing an iron soap is disclosed herein. The method comprising the steps of: reacting, at a temperature equal to or lower than a crystal transition initiation temperature of the iron soap to be manufactured, between a straight-chain saturated fatty acid alkali metal salt aqueous solution having from 12 to 22 carbons and a trivalent iron salt aqueous solution with pH of 0.1 to 5.5 so as to prepare an iron soap slurry; and adjusting pH of the prepared iron soap slurry to from 0.1 to 6.0.