Two important iron oxides: Fe3O4 and Fe2O3, as well as Fe3O4 and Fe2O3 nanoparticles mingling with Ag were successfully synthesized via a hydrothermal procedure. The samples were confirmed and characterized by X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The morphology of the samples was observed by transmission electron microscopy (TEM). The results indicated Fe3O4, Fe2O3, Ag/Fe3O4 and Ag/Fe2O3 samples all were nanoparticles with smaller sizes. The samples were modified on a glassy carbon electrode and their elctrocatalytic properties for p-nitrophenol in a basic solution were investigated. The results revealed all the samples showed enhanced catalytic performances by comparison with a bare glassy carbon electrode. Furthermore, p-nitrophenol could be reduced at a lower peak potential or a higher peak current on a glassy carbon electrode modified with Ag/Fe3O4 or Ag/Fe2O3 composite nanoparticles.