In this study, a simple compound (1 - x)(Bi0.5Na0.5)TiO3-xKNbO(3) (x = 0 - 0.12) lead-free bulk ceramic was developed for high electric power pulse energy storage applications. The dielectric and ferroelectric properties of the ceramics were measured. The results illustrate that the energy storage density of the ceramics is enhanced by the addition of KNbO3. The influence of applied electric field, temperature, and fatigue on the energy storage properties of the ceramics was evaluated for the composition-optimized (Bi0.5Na0.5)TiO3-0.1KNbO(3) ceramic. The results demonstrate that (Bi0.5Na0.5)TiO3-0.1KNbO(3) ceramic is a promising lead-free material for high power pulse capacitor applications. The excellent energy storage properties of the (Bi0.5Na0.5)TiO3-0.1KNbO(3) ceramics are ascribed to the reversible relaxor-ferroelectric phase transition induced by the electric field.