Extending the investigations on (Bi0.5Na0.5)TiO3-based solid solution for lead-free piezoelectric ceramics, this paper consider the complex solid-solution system (Bi0.5Na0.5)TiO3–(Bi0.5K0.5)TiO3 [BNT-BKT]. (Bi0.5Na0.5)TiO3 with 7~ 30 mol% (Bi0.5K0.5)TiO3 ceramics have been prepared following the conventional mixed oxide process. A morphotropic phase boundary (MPB) between rhombohedral (R) and tetragonal (T) was found at the composition 0.82BNT-0.18BKT with correspondingly enhanced piezoelectric properties. The electromechanical planar coupling factor is higher for compositions near the MPB. The mechanical quality factor (Qm), planar coupling coefficient (kp) and thickness coupling coefficient (kt) of 0.82BNT-0.18BKT ceramics were 125, 28.8% and 47.4%, respectively.