Polycrystalline Te-doped CoSb3 materials with various Te content have been obtained. The scanning microscope with the electron-probe microanalysis apparatus (EPMA) and XRD technique were used to investigate microstructures and to carry out the phase analysis. The Rietveld refinement method was used for refining structure parameters and for examining tellurium distribution in the CoSb3 structure. Thermoelectric properties have been investigated by means of the Seebeck coefficient, thermal, and electrical conductivity measurements. Optimal contents of Te for maximum figure of merit ZT have been determined. (C) 2002 K.T. Wojciechowski. Published by Elsevier Science Ltd. All rights reserved.