Highly (001) oriented (Ba,Sr)TiO3 thin films, grown on (001) LaAlO3 substrates by pulsed laser deposition, exhibit strong variation of strain over the thickness range of 20-800 nm. The tensile elastic residual strain reaches a minimum value at a thickness of 250 nm, while the inhomogeneous strain decreases gradually with increasing film thickness. The 250-nm-thick film has the largest in-plane dielectric constant due to a smallest tensile elastic strain in the film and the largest in-plane tunability of 40% is achieved in the thickest film (C) 2010 Elsevier B.V All rights reserved