The microscopic natures of structural stability and Li superionic conductivity of Li10GeP2S12 (LGPS) have been probed in this Letter by means of first-principles techniques. Our results suggest that the structural stability of LGPS is not only ascribed to the interionic Coulomb interaction, the Van Der Waals (VDW) interaction among polyhedra should also be emphasized. The distribution of Li ions in the LGPS has a strong impact on the system's structural stability. In addition, the superionic conductivity of the energetically favored LGPS has been investigated and confirmed, and it is suggested to be three-dimensional (3D) rather than one-dimensional (1D). (C) 2013 Elsevier B.V. All rights reserved.