The dependence of the ionic conductivity on the B-site ion substitution in (Li0.5La0.5)Ti1-xMxO3 (M = Sn, Zr, Mn, Gel system has been studied. The same valence state and various electronic configurations and ionic radii of Sn4+, Zr4+, Mn4+ and Ge4+ (4d(10) (0.69 Angstrom), 4p(6) (0.72 Angstrom), 3d(10) (0.54 Angstrom) and 3d(3) (0.54 Angstrom), respectively) induced the various crystallographic variations with substitutions. So it was possible to investigate the crystallographic factors which influence the ionic conduction by observing the dependence of the conductivity on the crystallographic variations. We found that the conductivity increased with decreasing the radii of B-site ions and vice versa and octahedron distortion disturbs the ion conduction. The reason for this reciprocal relationship of conductivity on the radius of B-site ions has been examined on the basis of the interatomic bond strength change due to the cation substitutions. The results were in good agreement with the experimental results. Therefore it could be concluded that interatomic bond strength change due to the cation substitutions may be one of the major factors influencing the lithium ion conductivity in the perovskite (Li0.5La0.5)TiO3 system.