The fifty seven turn thick La2O3 thin films were deposited on Si (100) substrates. After deposition, the amorphones thin films, were amorphous, were annealed at 750 and 900 degrees C for 1 h. It was found that their amorphous structure had been crystallized to hexagonal and cubic structures, respectively. The phase formation of the La2O3 thin films was anomalous at higher annealing temperatures. The theory of heterogeneous nucleation was used to interpret the anomalous phase formation of La2O3 films. To investigate the effects of the phase structure on these properties, Refractive indexes and dielectric constants of different structures of La2O3 films were measured. (C) 2008 Elsevier B.V. All rights reserved.