Newly gallo-titanogallate type KxGa8Ga8+xSn16-xO56 (KGGSO) was prepared by a solid state reaction and a flux slow-cooling method for exploring its potential as an ionic conductor. KGGSO single crystals were obtained under the following conditions: crystal composition "C" (K2CO3)(1)(Ga2O3)(8)(SnO2)(8); flux composition "F" (K2CO3)(2) (MoO3)(1)(B2O3)(1); "C/F" = 20/80; cooling rate, 4 K/h (1623 K-1273 K). The crystal had a needle-like morphology and averaged about 2 mm length and 10 mu m diameter. Structure refinement by single crystal X-ray diffraction showed reliability factors of R=0.0961 and wR=0.1481 under an isotropic condition. The lattice parameters of KGGSO (a = 1.8361(5) nm, c=0.31280(9) nm) were larger than those of K0.8Ga8Ga8.8Ti15.2O56 (KGGTO, a = 1.8135(2) nm, c=0.29966(4) nm). The chemical composition of KGGSO based on site occupancy was K1.436Ga8Ga8.764Sn15.236O56. In examining the cause behind the inhomogeneous expansion of the lattice parameter, we speculated that the potassium ions in the unit cell increased for keeping the gallo-titanogallate structure by substituting tin for titanium, and the repulsion force among potassium ions increased along the one-dimensional tunnels. Also, the KGGSO powder prepared at 1623 K for 24 h showed a solid solution region of 1.2 <= x <= 1.5 under the initial composition condition. (C) 2010 Elsevier B.V. All rights reserved.