Hydrophilic Fe3O4-Au Janus nanopartides have been synthesized through a facile aqueous solution-based Fe3O4 seed-mediated chemical reduction route, where Au nanoparticles can be in situ formed on surfaces of PVP-modified Fe3O4 nanoparticles by adopting the well-known citrate reduction route. The diameter of Au nanoparticles can be controllably tuned in the range of 3-12 nm by simply changing the initial molar ratio between Sodium citrate and auric acid. The as-fabricated hydrophilic Fe3O4-Au Janus naimpartides have shown excellent catalytic performance with high catalytic activity and recyclability due to the synergetic effect between Au and Fe3O4 nanoparticles.