Non-stoichiometric Sr beta-alumina single crystals were prepared in SrO-MgO-Al2O3 system by a. floating zone (FZ). method. The range of non-stoichiometry was determined as Sr1-0.25xMg1-xAl10 + x O-17 (+ 0.25x), where 0 < x less than or equal to 0.41. The lattice parameters of a increased and c decreased with increasing SrO content in the solid solution range. The single crystals had a cleavage plane parallel to the: (001) plane and growth direction. The electrical conductivity parallel and perpendicular to the cleavage plane showed maximum at x= 0.2 (i.e., 13.8 mol% SrO). The activation energy of electrical conductivity parallel to the cleavage plane (140 to 165 kJ/mol) was almost the same as that perpendicular to tire cleavage plane (150 to 170 kJ/mol). (C) 2003 Elsevier Science B.V. All rights reserved.