The polarization system and phase transition on Li_0.055(Na_0.50K_0.50)_0.945NbO₃ (LNKN) ceramics were investigated to determine the piezoelectric properties, relative permittivities and X-ray diffraction (XRD). The piezoelectric properties and relative permittivities were strongly dependent on the poled state, which poling temperatures were 25 or 150 °C. The XRD did not exhibit orthorhombic–tetragonal phase transition around the phase transition temperature because no orthorhombic phase was observed below the phase transition temperature. The LNKN ceramics had multiple poled states, the origin of the multiple poled states was considered to be attributable to the multiple spontaneous polarization (P _s) direction on perovskite structure. From these results, we proposed that the phase transition on LNKN was not an orthorhombic–tetragonal phase transition but a monoclinic-tetragonal phase transition. The monoclinic perovskite structure [Z=1, P m, a=3.9825(5) Å, b=3.9438(4) Å, c=4.0217(5) Å, β=90.292(3)°] can provide multiple P _s directions, such as [101]_pc and [001]_pc.