We have investigated effects of the postmetallization annealing and the electric field application on ferroelectric properties of BiFeO3 thin films prepared by chemical solution deposition. The leakage current is reduced after the postmetallization annealing although the crystallinity of the polycrystalline BiFeO3 is unchanged. In addition, double coercive field is reduced at about 90 kV/cm after the postmetallization annealing, while remanent polarization of 90 μC/cm2 is almost the same at 80 K. The postmetallization annealing is considered to lead the improvement of contact between the BiFeO3 film and the Pt electrode or the reduction in defects near the interface between the BiFeO3 film and the Pt electrode. Moreover, once a high electric field of 2.8 MV/cm is applied, the ferroelectric property of BiFeO3 thin films is dramatically improved. This effect may be due to the relaxation of pinned domains or locked polarizations in the BiFeO3 film. The postmetallization annealing and the electric field application are effective to improve ferroelectric properties of BiFeO3 thin films.