In ionic conducting materials, the crystal structure is closely related to the ionic conductivity. In this research we studied the microscopic features of Li0.5La0.5TiO3 which exhibited a lithium ionic conductivity as high as 1 x 10(-3) Scm(-1) at room temperature by XRD, TEM and SIMS. It was found that the superstructure was caused by the ordering of La+3 and vacancy, producing the 2a(p) x 2a(p) x 2a(p) unit cell. This ordering was found to be regular in microscopic region, but became irregular in macroscopic region. Li+ showed a random distribution which meet the needs for the fast ionic conduction. The second phase was found to be Li2TiO3 which existed in the grain boundary junctions.