The Fe3O4-graphene oxide (Fe3O4-GO) nanocomposites were prepared by a chemical co-precipitation of FeSO4, FeCl3,center dot NH3 center dot H2O and GO. The Fe3O4-GO was characterized by scanning electron microscopy. X-ray powder diffraction, thermogravimetric analysis and electrochemical method. The results showed that ultrafine Fe3O4 nanoparticles was prepared and densely assembled on GO nanosheets. The Fe3O4-GO exhibits large surface area and high catalysis towards the oxidation of cysteine and N-acetyl cysteine, which could be used for cysteine and N-acetyl cysteine sensing with a wide linear range (0.5-13.5 mM for cysteine and 0.12-13.3 mM for N-acetyl cysteine) and low detection limit (56 mu M for cysteine and 25 mu M for N-acetyl cysteine). The excellent catalytic activity, high sensitivity and good stability made such Fe3O4-GO nanocomposites to be promising nanomaterials for constructing nonenzymatic sensor. (C) 2012 Elsevier Ltd. All rights reserved.