La-doped BiFeO3 (BLFO) thin films have been deposited on Pt (Ill)/TiO2/SiO2/Si (100) substrates under different oxygen pressure of 5 mTorr -50 mTorr by the pulsed-laser deposition (PLD). The effects of oxygen pressure on crystal structure and ferroelectric properties have been investigated. X-ray diffraction analysis shows that the BLFO thin films are of pure perovskite phase with tetragonal structure. The dielectric constant of the films increases with increasing oxygen pressures. The film deposited at 10 mTorr is found to have a relatively high dielectric constant and a relatively small dielectric loss. It also shows a low value of leakage current 1.17 x10-7 A/cm2 at a field strength of 100 kV/cm and ferroelectric properties at room temperature.