Ferroelectric BaTiO3 thin films have been prepared by laser ablation on heated (100)SrTiO3 substrates under different oxygen pressures, i.e. 0.7, 7 and 70 Pa. The films grown at 0.7 and 7 Pa are c-axis oriented, while the film grown at 70 Pa is a-axis oriented. The lattice constants of the films normal to the substrate surface are 4.0566, 4.0280 and 3.9972 Angstrom, respectively. The surface morphology of the films observed under the scanning force microscope is relatively smooth at 0.7 Pa but rougher at 7 Pa and the grains of the film become very rough at 70 Pa. The root mean square roughness increases from 1.22, to 3.44 to 6.39 nm. The results show that by varying the oxygen pressures and maintaining all the other conditions constant, it is possible to control the orientation, lattice parameters and surface morphology of the BaTiO3 thin films.