The predominant factors of the activation energy for ionic conductivity in perovskite-type lithium ion-conducting oxides were discussed in terms of structural distortion. As the result, the activation energies in almost all compounds are governed by a factor, a p /(B large -O) (a p : perovskite parameter (cube root of cell volume per formula unit), (B large -O) : inter-atomic distance between larger B ion and oxygen ion). This finding implies that (i) the larger B ion gives rise to structural distortion such as the tilt of the BO 6 octahedra, which decrease the bottleneck size, (ii) the resultant smaller bottleneck determines the activation energies for ionic diffusion.