A synchrotron X-ray powder diffraction pattern was measured for a lithium superionic conductor, Li7P3S11 It, which has a high conductivity of 3.2 x 10(-3) S em- 1 at room temperature and a low activation energy of 12 U mol- 1 [Mizuno et al., Solid State Ionics, vol. 177 (2006) 272 1]. The crystal structure was solved by a direct space global optimization technique and refined by the Rietveld method. The compound crystallizes in a triclinic cell, space group P- 1, alpha = 12.5009(3) A, beta = 6.03160(17) A, gamma - 12.5303(3) A, o(= 102.845(3)degrees, 113.2024(18)degrees, 74.467(3)degrees. PS4 tetrahedra and P2S7 ditetrahedra are contained in the structure and Li ions are situated between them. (c) 2007 Elsevier B.V. All rights reserved.