Barium strontium titanate (BST) thin films were prepared by RF magnetron sputtering. The curves of dielectric constant-voltage, dissipation factor-voltage and the hysteresis loops of BST thin films with different grain sizes were investigated. The differences of the curves were analyzed. The voltage shift and an increase in the maximum dielectric constant were observed in ε- V curves as the grain size in the films increased. It is found that the dielectric loss of BST thin films does not change significantly with applied voltage. The origin of the asymmetric hysteresis due to asymmetrical potential barriers at the upper and bottom interfaces, residual elastic stress and incomplete compensation of depolarizing field was discussed. © 2004 Elsevier B.V. All rights reserved.