Nanocrystalline tin oxide (n-SnO2) with different grain sizes were synthesized by chemical precipitation method. Size variation was achieved by changing the hydrolysis processing time. Structural phases of the nanocrystalline SnO2 were identified by X-ray diffraction (XRD). The grain sizes of the prepared n-SnO2 were found to be in the range 5-20 nm which were estimated using the Scherrer formula and they were confirmed by transmission electron microscopy (TEM) measurements. The electrical properties of nanocrystalline SnO2 were studied using impedance spectroscopy. The impedance spectroscopy results showed that, in the temperature range between 25 and 650 degrees C, the conductivity has contributions from two different mechanisms, which are attributed to different conduction mechanisms in the grain and the grain boundary regions. This is because of the different relaxation times available for the conduction species in those regions. However, for the temperatures above 300 degrees C, there is no much difference between these two different relaxation times. The Arrhenius plots gave the activation energies for the conduction process in all the samples. (c) 2005 Elsevier B.V. All rights reserved.