Tin oxide (SnO2) nanocrystals have been synthesized by two-step solid-state reactions. In the first step, the SnO fine particles are synthesized from the reaction of SnCl(2)(.)2H(2)0 precursor with KOH in the size range of ca. 500 nm. Then the fine particles are oxidized into nano-sized SnO2 crystals with O-2. It is an environment friendly, convenient, inexpensive and efficient preparation of SnO, nanocrystals with grain size of ca. 20nm. The prepared SnO2-based gas sensors have an excellent ability of discriminating EtOH from gasoline. (C) 2002 Elsevier Science B.V. All rights reserved.