In order to improve the ionic conductivity of lithium in the (Li, La)NbO3 perovskite system due to the expansion of the lattice, we attempted to prepare three perovskite compounds (Li0.05La0.317)(1-x)Sr0.5xNbO3, (Li0.1La0.3)(1-x)Sr0.5xNbO3 and (Li0.25La0.25)(1-x)Sr0.5xNbO3 by the substitution of larger Sr2+ ions for smaller Lif ions and La3+ ions in Li0.05La0.317NbO3 (orthorhombic), Li0.1La0.3NbO3 (tetragonal) and Li0.25La0.25NbO3 (cubic), respectively. Also, the perovskite compounds (Li0.25La0.25)(1-x)Ca0.5xNbO3 were prepared by the substitution of smaller Ca2+ ions for larger La3+ ions for comparison. The enhancement of lithium ionic conductivity was confirmed in all the Sr2+ doped perovskite compounds because of the increase of the cell volume. Especially, the perovskite (Li0.25La0.25)(1-x)Sr0.5xNbO3 exhibited marked improvement of ionic conductivity (x = 0.125, 7.3 x 10(-5) S.cm(-1) at 25 degrees C) compared with that of the other perovskites ((Li0.05La0.317)(1-x)Sr0.5xNbO3 and (Li0.1La0.3)(1-x)Sr0.5xNbO3), on the contrary, the ionic conductivity of (Li0.25La0.25)(1-x)Ca0.5xNbO3 perovskite compounds decreased with increasing the amount of calcium due to the decrease of the cell volume.