The Relationship between the Piezoelectric Properties and Crystal Lattice Deformation and Distortion Resulting from the Li Substitution in Li_XNa_0.52K_0.48-XNbO₃, Alkaline Niobate-Based Perovskite Ceramics of (Li, Na, K)NbO₃, Was Investigated. the Lattice Parameters of the Sample with a Li Content X = 0.05 and Having a Monoclinic System with Space Group PM Were a = 3.9789(6) Å, B = 3.9385(5) Å, C = 4.0134(6) Å, and B = 90.305(4)º. the E^T33/e0, Kr, and -D31 Values of the Sample by Poling in the Monoclinic System Were 450, 44.6%, and 57 PC/N, Respectively. on the other Hand, the E^T33/e0, Kr, and -D31 Values of the Sample by Poling in the Tetragonal System Were 600, 38.7%, and 56 PC/N, Respectively. the Remarkable Piezoelectric Properties of these Ceramics Can Be Attributed only to the Low Symmetry of their Monoclinic System, which Is a Subgroup of aMm2 and P4mm. Li_0.05Na_0.52K_0.43NbO₃ Ceramics with a Monoclinic System Were Observed to Have the Unique Piezoelectric Characteristics.