The average structure and microstructure of a lithium-ion conducting perovskite La2/3-xLi3xTiO3 (x = 0.12) were investigated using neutron diffraction and transmission electron microscopy (TEM). The obtained results were compared with those of previous studies on La2/3-xLi3xTiO3 series compounds, and the relationship between their structures and ionic conduction was discussed. The Rielveld refinement using neutron diffraction data reveals that the average structure (space group: Cmmm) of furnace-cooled Li-rich La2/3-xLi3-xTiO3 (x=0.12) involves alternative ordered arrangement of La along the c-axis and anti-phase-tilt of TiO6 octahedra along the b-axis as with Li-poor La2/3-xLi3-xTiO3(x=0.05). It was found that the strong correlation between structure and percolative diffusion pathways in the perovskites is primarily referred to the ordered arrangement of La ions, and the "bottleneck" square-surrounded by four oxygen ions determined by the distortion and tilt of TiO6 octahedra. In addition, the 90 degrees-oriented micro-domain structure, which also influences the percolative diffusion pathways in La2/3-xLi3xTiO3, was observed by TEM. (c) 2006 Elsevier B.V. All rights reserved.