Dependence of electrical properties on the structural characteristics of Li 0.04 (K 0.5 Na 0.5 ) 0.96 (Nb 1−y Sb y )O 3 (LKNNS (x=0, 0.00≤y≤0.10)) and [Li 0.04 (K 0.5 Na 0.5 ) 0.96−x Ag x ](Nb 0.925 Sb 0.075 )O 3 (LKNANS (0.01≤x≤0.05, y=0.075)) were investigated. The oxygen octahedral distortion was dependent on Ag + and/or Sb 5+ content which affected to the phase transition temperature of LKNNS and LKNANS ceramics. The orthorhombic–tetragonal and tetragonal–cubic phase transition temperatures (T O–T , T C ) of the specimens were decreased with increasing of average octahedral distortion. With increasing of Sb 5+ content, the electromechanical coupling factor (k p ), piezoelectric constant (d 33 ) and dielectric constant (ɛ r ) of the sintered specimens were increased up to y=0.075, and then decreased. These results could be attributed to the shift of T O–T to near room temperature for Li 0.04 (K 0.5 Na 0.5 ) 0.96 (Nb 0.0925 Sb 0.075 )O 3 .