We performed spectroscopic ellipsometric measurement to characterize BaSm2Ti4O12 (BST) thin films grown on Pt/Ti/SiO2/c-Si substrate by rf magnetron sputtering. The six BST films were prepared at various deposition temperatures and thermal annealing times. The resulting refractive indices and extinction coefficients of the BST films show only slight change by the deposition temperature but a significant change after thermal annealing, implying the importance of the post annealing process. The increase of the refractive index can be understood by the higher density of the BST films caused by the crystallization after annealing process. (C) 2009 Elsevier B.V. All rights reserved.