Lead-free potassium sodium niobate piezoelectric ceramics substituted with lithium and antimony (Na0.5 K0.5) 1-x (LiSb)x Nb1-x O3 have been synthesized by conventional solid state sintering method. Compositionally engineered around the orthorhombic-tetragonal polymorphic phase transition, the dielectric and piezoelectric properties were further enhanced with the addition of lithium and antimony substituted into the perovskite structure. The combined effects of lithium and antimony additions resulted in a downward shift in the orthorhombic-tetragonal (TO-T) without significantly reducing TC. The dielectric, piezoelectric, and electromechanical properties were found to be �� ��0 1300, d33 260 pCN, and kp 50%, while maintaining low dielectric loss. The enhanced polarizability associated with the polymorphic TO-T transition and high TC transition (���390 ��C) should provide a wide range of temperature operation. �� 2006 American Institute of Physics.