Well-crystallized Ba(Fe1/2Nb1/2)O3 thin films were grown on Pt/TiO2/SiO2/Si substrates in various oxygen pressures at 550 °C by pulsed laser deposition. X-ray diffraction analysis revealed that the thin films had a single phase of perovskite structure. The lattice constants of thin films increased obviously with decreasing the deposited oxygen pressure due to more oxygen deficiency in samples. Saturated polarization-electric-field (P-E) loops and butterfly-shaped capacitance-voltage (C-V) curves were observed in Ba(Fe1/2Nb1/2)O3 thin films at room temperature. The remnant polarization decreased with increasing the deposition oxygen pressure and was further depressed by annealing in high pressure oxygen. The oxygen vacancy played a predominant role in the ferroelectricity of Ba(Fe1/2Nb1/2)O3 thin films.