Effects of both phase boundaries and poling conditions on the piezoelectric activity of (K,Na)NbO₃ (KNN)-based ceramics {e.g., (1 − x) (K_0.42Na_0.58) (Nb_0.96Sb_0.04)O₃–x(Bi_0.5K_0.5)_0.90Zn_0.10ZrO₃ [(1 − x)KNNS–xBKZZ]} were studied in detail, and their d₃₃ was promoted by refining the phase compositions and choosing optimum poling conditions (i.e., poling temperature, poling electric field, and second-poling process). The rhombohedral-tetragonal phase boundary was formed in the ceramics with 0.04 < x ≤ 0.05. In addition, their piezoelectric activity was further promoted by optimizing the poling temperatures and poling electric fields as well as the second-poling methods. The ceramics with x = 0.045 have enhanced piezoelectric activity (e.g., d₃₃ ∼ 425 pC N⁻¹ and k_p ∼ 47%), and both d₃₃ (425 pC N⁻¹) and T_C (248 °C) of this work can match well that (d₃₃ ∼ 416 pC N⁻¹ and T_C ∼ 253 °C) of textured (Na,K,Li)(Nb,Ta,Sb)O₃ ceramics. It is worth noting that a large strain (0.297%, S_max/E_max = 582 pm V⁻¹) was also found in the ceramics with x = 0.04, which is superior to currently reported results in KNN-based ceramics.