New lithium ion conductors of perovskite-type compounds R1/4Li1/4TaO3 (R = La, Nd, Sm and Y) were synthesized, and their crystal structure and Lithium ion conductivity were characterized. Symmetry of the perovskite lattice changed from cubic for La1/4Li1/4TaO3 to tetragonal for Nd1/4Li1/4TaO3 and Sm1/4Li1/4TaO3, and to orthorhombic for Y1/4Li1/4TaO3. The alternate ordering of R and Li ions and vacancies at the A-sites was observed for Nd1/4Li1/4TaO3, Sm1/4Li1/4TaO3 and Y1/4Li1/4TaO3. The cube root (V-1/3) of the subcell volume decreased with decreasing the ionic radius of R cations which act as spacers for the perovskite lattice. With decrease in V-1/3 from La1/4Li1/4TaO3 to Y1/4Li1/4TaO3, the bulk conductivity at 400 K decreased from 1.4 x 10(-1) S m(-1) to 5.0 x 10(-7) S m(-1) and its activation energy increased from 0.35 eV to 0.85 eV. The subcell volume and the ordering at the A-sites are major factors in influencing lithium ion conduction in these perovskite-type conductors.