Thin films of barium strontium titanate are fabricated on alumina by a hydrothermal method. Crystalline films are produced at temperatures as low as 60°C. The relative dielectric permittivity of films with the composition Ba0.15Sr0.85TiO3 lies in the range between 150 and 220 for low frequencies (100 kHz to 1 MHz), decreasing with frequency. The loss tangent for the films increases from 0.05 to 0.15 over the same frequency range. Relative concentrations of barium and strontium in the film are controllable through the hydrothermal reaction conditions. The surface microstructure of the films is examined.