The Li+ concentration in nominal Li7Al0.25La3Zr2O12 (LALZO) solid electrolyte are believed to pose significant effect on its electrical conductivity. The affecting mechanism of Li+ concentration on microstructure evolution and its relationship with Li ionic conductivity is investigated. Results show that Li+ occupancy in octahedral site (LiO6) increases with the increase of Li+ concentration and Li+ arrangement becomes a certain degree ordered in tetragonal site (LiO4) at 6.72 moles Li+ concentration. The structural evolution indicates that higher Li+ concentration in LiO6 as well as disordered Li+ arrangement in LiO4 will enhance the grain conductivity which infers the best Li+ concentration of 635 moles. The tested electrical property show the highest grain ionic conductivity of 1.35 x 10(-3) S cm(-1) at Li+ concentration of 6.35 moles which is in good agreement with prediction made from the structural evolution. It is concluded that Li+ concentration affects Li ionic conductivity via changing Li+ distribution in the grain. (C) 2015 Elsevier B.V. All rights reserved.