The synthesis of LaxAl2-xO3 films using ultrasonic spray pyrolysis technique are reported. The films were deposited from a spraying solution of aluminum acetylacetonate (Al(acac)3) and lanthanum(III) nitrate hexahydrate La(NO3)36H2O dissolved in N,N-Dimethylformamide on (100) Si substrates. The substrate temperature during was in the range 500-600°C. The mean roughness was lower than 18 Å in all cases. The films were amorphous in all cases. The optical band gap was 5.42 eV and the refractive index was in the 1.64-1.72 range depending of the deposition conditions.