BiFeO3 is a multiferroic material with physical properties very sensitive to its stoichiometry. BiFeO3 thin films on silicon substrate are prepared by the sol–gel method combined with layer-by-layer annealing and final annealing schemes. X-ray diffraction and scanning electron microscopy are employed to probe the phase structures and surface morphologies. Using Rutherford backscattering spectrometry to quantify the nonstoichiometries of BiFeO3 thin films annealed at 100?C–650 ?C. The results indicate that Bi and Fe cations are close to the stoichiometry of BiFeO3, whereas the deficiency of O anions possibly plays a key role in contributing to the leakage current of 10?5 A/cm2 in a wide range of applied voltage rather than the ferroelectric polarizations of BiFeO3 thin films annealed at high temperature.