(LaxN1-3x-yLiy square(2x)NbO(3) (0.1 less than or equal to x less than or equal to 0.2, 0.1 less than or equal to y less than or equal to 0.2) have been prepared by the conventional solid-state technique. Their lattice parameters and AC complex impedance were measured. Synthesized samples showed cubic symmetry. Lattice parameters decreased with increasing lithium content y. The values of complex impedance became smaller with rising temperature and increasing lithium concentration. Among (LaxNa1-3x-yLiy square(2x)) NbO3 (0.1 less than or equal to x less than or equal to 0.2, 0.1 less than or equal to y less than or equal to 0.2), (La(0.2)Na(0.16)Li(0.13)square(0.51))NbO2.95 is the best ionic conductor, and it shows ionic conductivity of 3.9 x 10(-6) S cm(-1) at room temperature.