The phase transitional behavior and composition-dependent piezoelectric properties of (NaK)(NbSb)O-3-LiTaO3-BaZrO3 (NKNS-LT-BZ) pseudo-ternary system were investigated. A composition-temperature phase diagram was generalized within a certain range of BZ content in which a rhombohedral-tetragonal (R-T) ferroelectric phase boundary connecting orthorhombic and cubic phase zones is formed near room temperature between two trifurcate points. Piezoelectric and electromechanical properties of NKNS-LT-BZ ceramics exhibit optimum values of d(33) = 365 pC/N and k(p) = 45% in the vicinity of the R-T phase coexistence zone. The dielectric and ferroelectric properties and the phase transition of NKNS-LT-BZ ceramics were discussed from a crystallographic point of view.