The basic aim of our study is to investigate the correlation between structural parameters and the electrocaloric effect in lead-free epitaxial Ba_1−xSr_xTiO₃ (BSTO) based thin film architectures. Therefore, BSTO thin films with Sr contents of x = 0 to x = 0.3 were grown on SrRuO₃ buffered SrTiO₃ single crystalline substrates by pulsed laser deposition. Structural characterization verified an epitaxial growth for all Sr contents with an additional tetragonal distortion compared to bulk material. Temperature and frequency-dependent measurements of dielectric properties revealed increased permittivity values for thicker films with broad maxima indicating a diffuse phase transition. The temperature of maximum permittivity decreases with increasing Sr content, whereas polarization measurements indicate a relaxor-like behaviour in particular above room temperature. Adiabatic temperature changes were determined with the indirect method resulting in |ΔT| values of up to 2.9 K for a 680 nm thick BSTO layer with x = 0.3 at an applied electric field of 750 kV cm⁻¹.