Effect on the ionic conductivity of B-site ion (M) substitution in (Li3xLa2/3-x)(1+y/2)MyTi1-O-y(3) (M=Al, Cr) has been investigated. It has been found that partial substitution of smaller Al3+ for Ti4+ is effective to enhance the ionic conductivity of Li3xLa2/3-xTiO3. At 300 K, the maximum bulk conductivity of (1.58+/-0.01) x 10(-3) S cm(-1) is observed from the composition of (Li0.39La0.54)(1-y/2)AlyTi1-yO3 with y = 0.02 (x = 0.13), that is the highest yet reported for known perovskite solutions at room temperature. The conductivity enhancement is interpreted as being due to the substitution-induced bond-strength change rather than due to bottleneck size change for Li migration, TiO6-octahedron tilting or A-site cation ordering. (C) 2003 Elsevier Science Ltd. All rights reserved.