High quality La1-xBaxMnOz (LBMO) thin films were successfully grown by the ion beam sputtering method for the first time on MgO and LaAlO3 (LAO) substrates simultaneously with a supply of molecular oxygen at a substrate temperature (T-s) of 700 degreesC. These films exhibit a single phase and good crystallinity. Effects of oxygen partial pressure (Po) on the crystallinity and c-parameter are studied systematically. The full-width at half-maximum (FWHM) averaged over (0 0 1) and (0 0 2) X-ray diffraction peaks shows a minimum at Po around 2 mTorr for the films grown on MgO. At this Po, FWHM for the films grown on MgO substrate is about 3 times less than that for the films grown on LAO substrate. This indicates that better crystalline films can be grown on MgO in this particular window of P-0 similar to2 mTorr. The c-parameter values are much smaller for the films grown on MgO as compared to LAG.