Fe²⁺ cations in FeCl₂ or FeSO₄ were oxidized by graphene oxide, leading to an in situ deposition of Fe₃O₄ nanoparticles onto the self-reduced graphene oxide (rGO) sheets. The resultant Fe₃O₄/rGO sheets were demonstrated to possess interesting magnetic and electrochemical properties attractive for a large variety of potential applications.