A combined sintering aid mixture of B(2)O(3) and CuO for lead-free piezoelectric ceramics having the composition 0.95K(0.5)Na(0.5)NbO(3)-0.05BaTiO(3) (KNN-BT) is introduced. The effects of the sintering aid mixture of 0.6B(2)O(3)-0.4CuO on the sintering behavior, microstructure, and electrical properties of KNN-BT are investigated. Adding 2 wt% of the sintering aid mixture can effectively broaden the narrow sintering temperature range having a size of 20 degrees C to above 50 degrees C and increase the grain size of samples as well as maintain the high density of samples sintered at a low temperature. The increase in grain size contributes to an improvement in electrical properties. High piezoelectric properties of d(33) = 205 pC/N, k(p) = 38.0%, Q(m) = 119, epsilon(T)(33)/epsilon(0) = 1254, and tan delta = 0.0264 are obtained for a KNN-BT-2wt% (B(2)O(3)-CuO) sample sintered at 1120 degrees C.