Lead-free piezoelectric ceramics (K0.45Na0.55)NbO3 (KNN) modified by K4CuNb8O23 (KCN) were synthesized using conventional ceramic processing. All the ceramics possessed the perovskite structure with orthorhombic symmetry. Results revealed that the addition of KCN was effective in enhancing the density of KNN. The addition of KCN was found to slightly decrease To-t and T-c. The coercive field (E-c) was found to maintain the same value by the addition of KCN while the internal bias (E-i) sharply increased to 4 kV/cm with 0.5 mol% KCN. The low migration rate of defect dipoles was correlated with the build-up of E-i, which was responsible for the stabilization of the domain wall and the improvement of Q(m). Therefore, KNN-KCN0.5 exhibited excellent piezoelectric properties of d(33) (100 pC/N), k(p) (33%), and Q(m) (1500), making them promising candidates for applications requiring hard piezoelectrics.