We grew single crystals of K1.88Ga1.88Sn6.12O16 hollandite-type compound and precisely determined their crystal structure by X-ray diffraction. K1.88Ga1.88Sn6.12O16 fibrous crystals measuring an average of about 2 mm in length and 60 mu m in diameter were obtained by slowcooling (from 1623 K to 1273 K) of a flux melt consisting of a 40 mol% crystal composition of (K2O)(1)(Ga2O3)(1)(SnO2)(1) and a 60 mol% flux composition of (K2O)(2)(MoO3)(1)(B2O3). The unit cell of K1.88Ga1.88Sn6.12O16 (a=1.0389(2) nm, c=0.3132(2) nm, V=0.3381(2) nm(3)) was larger than that of K1.52Ga1.52Ti6.48O16. The ionic size difference with the replacement of Ti by Sn, 10%, was relaxed by an anisotropic expansion of the octahedra by 2.6% in the (001) plane and 5.8% along the c-axis. (c) 2006 Elsevier B.V. All rights reserved.