Au/Fe3O4 nanocomposites were prepared by anchoring gold nanoparticles onto Fe3O4 support surfaces. First, spherical gold nanoparticles was synthesised via a reducing method with hydroquinone as reductants. Then, Fe3O4 supports were synthesized by a solvothermal method and modified by mercaptopropionic acid (MPA). At last, gold nanoparticles were immobilized on the surface of Fe3O4 support using MPA as a linker,. The morphology, crystallinity, magnetism and catalytic activity of the Au/Fe3O4 nanocomposites were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, vibrating sample magnetometry (VSM) and UV–Vis spectrophotometer (UV-vis). The results indicate that the surface of the Au/Fe3O4 composite is coated with gold nanoparticles (NPs), the nanocomposites are monodisperse and supermagnetic, and show an excelently catalytic activity in the reduction of 4-nitrophenol to 4-aminophenol with sodium borohydride.