Ferroelectric Ba1−xSrxTiO3thin films were deposited by pulsed laser ablation on SiO2/Si, RuO2/Ta/SiO2/Si and Pt/Ti/SiO2/Si substrates. The films were weakly crystalline in the as-deposited condition and subsequent crystallization was induced by annealing the films in the range of 550–650°C. The BST films deposited on Pt/Ti/SiO2/c-Si substrates presented wide cracks that were promoted during the annealing process due to the thermal expansion mismatch between the BST films (αBST= 4 × 10−6°C−1) and the Pt (αPt= 9 × 10−6°C−1). Smooth films showing slightly crackeded areas were obtained on SiO2/c-Si and RuO2/Ta/SiO2/Si substrates. The ruthenium oxide thermal expansion coefficient is αRuO2= 5.2 × 10−6°C−1. A cross-sectional analysis at the ferroelectric/substrate interface showed that for the lower annealing temperature (550°C) a mixed amorphous/nanocrystalline microstructure is formed. For temperatures above 600°C a randomly oriented polycrystalline material is obtained. However, an amorphous layer of 4–6 nm still remains on the substrate even after heat-treatments up to 650°C. The dielectric constant of the BST films varied in the range of 30–325.