The bismuth layer-structured ferroelectrics (BLSFs) sodium-potassium bismuth titanate (NaxK1 - x)0.5Bi4.5Ti4O15 polycrystalline ceramics with cobalt substitution were synthesized using conventional solid-state processing. The phase structure, microstructural morphology, and electrical properties of NKBT ceramics with different Na/K ratio were investigated in detail. The substitutions of Na for K in NKBT ceramics cause the decrease in unit cell volume, resulting in the diffraction peaks shift to higher angles. The piezoelectric activities, electromechanical properties, and remnant polarization were found to be enhanced with the increasing ratio of Na/K. The Curie temperature Tc of NKBT piezoelectric ceramics was found to linearly increase from 578 degrees C to 670 degrees C with the increasing ratio of Na/K, which is ascribed to the small ionic radius of Na+ ions in comparison with K+ ions. The large piezoelectric activities and high electromechanical properties, together with high Curie temperature, make NKBT ceramics promising for high-temperature piezoelectric applications.