[en] Hydrophilic iron oxide Fe₃O₄ nanoparticles (NPs) were prepared by a reverse micro-emulsion method. Functionalization of Fe₃O₄ NPs was then carried out via surface graft polymerization to achieve outstanding magnetic property. Characterization results indicate that grafted core–shell Fe₃O₄ displayed inverse spinel crystalline structure, while particle size and it’s distribution were controlled accordingly. The ferromagnetic behavior (60 A m² kg⁻¹) of grafted Fe₃O₄ NPs was restored close to bulk value through enhancement of Fe–O ionic bond.