Amorphous aluminum oxide films were deposited by the pyrosol process using aluminum acetylacetonate as source material dissolved in a mixture of three parts of deionized water and one part of methanol. An accelerator ion beam analysis technique was used to obtain the areal density and the chemical composition of the aluminum oxide films, which result in being oxygen-rich when films are deposited at a substrate temperature of 480 degrees C. The infrared spectra show a broad-absorption band from 400 to 1000 cm(-1) typical of the vibrations of the Al2O3. LR analysis also shown that then are no O-H or alanol (Al-OH) groups incorporated in the films and that films kept at air atmosphere at room temperature have a high stability against water adsorption. The refractive index of the films measured by ellipsometry was 1.647. The optical transmission has a value of the order of 88% in the range from 400 to 900 nm for films deposited onto pyrex glass and fused quartz slices. There is no optical absorption edge for wavelengths around 190 nm, which indicates that the deposited films have an energy band gap of at least 6.2 eV. The current density-electric field characteristics of MIM structures, incorporating insulating aluminum oxide films, show current injection across the film for electric fields higher than 2 MV/cm. Electric breakdown was not observed for applied electric fields of the order of 4.5 MV/cm.