[Object] To provide a polymer coated ferrite fine particles being possible to control a particle size uniformly while having high aqueous dispersibility and preferred biomolecule immobilization ability and an easy method for preparing the same.[Means Addressing Object] In an aqueous solvent, iron ion is protected by chelating polyacrylic acid and then alkaline is added. Thereafter, a reaction system is heated under pressurized condition to produce simultaneous precipitation of the ferrite fine particles and coating thereof. As the result, the polymer coated ferrite fine particles having uniform particle size may be prepared in one step with excellent reproducibility. The polymer coated ferrite fine particles of the present invention has high water dispersibility and has preferred biomolecule immobilization performance by carboxyl groups coming from the polyacrylic acid.