In the dielectric (Ba,Sr)TiO3 thin films, the correlation between the film thickness and the dielectric properties was investigated. The dielectric properties such as the dielectric constant (epsilon) and dielectric loss (tan delta) were measured using the capacitor geometry. As the film thickness increased, the dielectric constant also increased due to the reduction of the interfacial dead-layer effect. However, the dielectric loss did not show a monotonous variation with the increasing film thickness. It was found that the dielectric loss correlated well with the non-uniform distribution of local strain, as analyzed by X-ray diffraction, according to the Curie-von Schweidler relaxation law. (c) 2006 Elsevier B.V. All rights reserved.