For the deposition of (K0.48Na0.52)NbO3 (KNN) thin films, excessive K and Na are added in precursor to compensate their volatilization during annealing process. In this work, the effects of excessive K and Na on the dielectric and leakage current properties of the KNN films were studied systemically. The leakage current and dielectric properties of the KNN films are strongly affected by excess amounts of K and Na as well as the annealing conditions. When K and Na are excessive by 6 mol% and 17 mol% respectively, the KNN(6,17) thin films show the smallest leakage current density of 1.8 x 10(-6) A/cm(2) at 50 kV/cm and the lowest dielectric loss of 3.3%. (C) 2013 Elsevier B. V. All rights reserved.