This work presents a physicochemical analysis of the characteristics of high-k lanthanum aluminate LaAlO3 (LAO) that is deposited on indium tin oxide (ITO)/glass substrates by pulsed laser deposition at various oxygen pressures and then undergoes low-temperature post-deposition annealing (PDA). Samples that are deposited at a low oxygen pressure of 0.067 Pa have a higher leakage current density than samples deposited at 0.27 Pa oxygen pressure owing to the imperfect stoichiometry of LAO that rises from deficient oxygen atoms in LAO. The leakage current increased with the oxygen pressure over 0.27 Pa because of the degradation of either surface roughness of LAO or the interfacial layer that is composed of a mixture of metal oxides. PDA treatment at a low temperature of 200 or 300 °C in O2 was applied to samples that were deposited at an oxygen pressure of 0.27 Pa. These samples had a relatively low leakage current density. PDA treatment at 300 °C improved the leakage current density of samples by approximately an order of magnitude at an electrical field of 1 MV/cm. The incorporation of oxygen atoms during PDA at 300 °C in O2 ambient increases breakdown field of capacitors with an Al/LAO/ITO structure from 7 to 14 MV/cm by reducing the surface roughness of LAO and improving the stoichiometry and bond structures of the LAO films.