The reduction-resistant properties of piezoelectric ceramics are of great importance for multilayer monolithic structures based on base metal inner electrodes, particularly for recently reported niobate-based lead-free perovskites. In this letter, the Hall-effect measurement and impedance analysis indicate that conventional (K,Na)NbO3 (NKN)-based ceramics exhibit an n-type electronic conduction. Rapid increase in the concentrations of oxygen vacancies and electrons is responsible for severe degradation of resistivity and piezoelectric properties as sintered in N-2. By comparison, p-type NKN-based ceramics by Mn doping exhibit excellent electrical properties (d(33) = 368 pC/N, d33* = 643 pm/V, tan delta = 0.019, and IR = 39.9 G omega center dot cm) in N-2 sintering atmosphere, as well interpreted by a series of proposed defect chemistry equations. The experimental results suggest that an introduction of the p-type conduction behavior should be an effective strategy to enabling NKN-based ceramics and Cu/Ni electrodes to well co-fire in a weakly reducing atmosphere.