PURPOSE: To obtain a magnetic ink having a high magnetization intensity in a low magnetic field and in a black solution, by adding surfactant to an aqueous suspension of Mn-Fe ferrite powder, acidifying the resultant mixture, and dispersing acidified mixture in an oil.

CONSTITUTION: A surfactant, e.g. sodium oleate, consisting of a unsaturated fatty acid (salt) is added to an aqueous suspension of fine Me-Fe ferrite powder having the composition of 35W60mol% Fe2O3, 1W60mol% FeO and 1W64mol% MnO prepared by the wet method. An acid is then added thereto to give an acidic aqueous solution having a pH of 7W5. The resultant flocculate is then filtered and washed with water or a polar solvent, dehydrate and then dispersed in a solvent of low polarity, e.g. kerosene.