The dielectric properties of KTaO3 and KNbO3 I-V perovskite thin films grown by hydrothermal epitaxy on conducting SrTiO3 substrates are presented. As-grown films exhibited frequency dispersion of dielectric properties and high tangent losses associated with adsorption of hydroxyl groups and lattice proton incorporation respectively. Three post deposition treatments were investigated to improve the dielectric properties of the films. Thermal annealing at 600 degrees C and oxygen plasma treatment were effective in eliminating lattice hydroxyls and adsorbed groups. Ozone treatment improves dielectric loss only marginally. (C) 2007 Elsevier B.V. All rights reserved.