The low-temperature sol-gel method has been used to prepare two types of thin films on low-resistivity silicon substrates: one of pure SiO2 arid the other containing 1% by weight of aluminum oxide particles embedded in the SiO2 matrix. The average size of the alumina particles was of 0.2 mu m. The Al2O3 particles were added in the starting solution. Pure SiO2 dielectric films were prepared using four different solutions of tetraethyl orthosilicate, water; and ethanol, whereas the films with the aluminum oxide particles were prepared with only one composition. To study the film properties, electric impedance, atomic force microscopy, optical microscopy, ellipsometry, and infrared absorption measurements were used. The dependence of the dielectric properties of the films on the relative amount of the components in the starting solution (in particular, on the presence of the particles of Al2O3) and on the corresponding subsequent thermal treatment was investigated. A correlation was found between the film structure and its quality as a dielectric coating. It is shown that the method employed allows the preparation of films with dielectric characteristics close to those of the thermally grown silicon oxide.