Tantalum oxide and tantalum - aluminum oxide films have been prepared by pyrosol using alcoholic start solution of tantalum chloride and aluminum acetylacetonate at substrates temperatures of 250 degrees C. All films are amorphous independent of the deposition conditions. X-ray diffraction shows that aluminum incorporation in deposited materials stabilizes the amorphous phase even after annealing at 525 degrees C and 900 degrees C. Energy dispersive spectroscopy, Rutherford backscattering, refractive index, and FTIR results indicate that the relative chemical composition of the deposited films is about [Ta] = 20 atom % and [O] = 80 atom %, probably containing hydroxide or oxohydroxide groups. The concentration of aluminum in films depends on the concentration of aluminum acetylacetonate in start solution with a ratio [Al atom % in film]/ [ Al atom % in solution] approximate to 0.1. The rms roughness has values of < 1 nm. The effect of incorporation of aluminum in deposited material and its annealing at 525 degrees C on the electrical characteristics of metal-oxide - metal structures increases the breakdown electric field and decreases the current density. The dielectric constant decreases as the aluminum concentration increases and annealing has a densification effect on the TAO films. (c) 2007 The Electrochemical Society.