Three different SnO2-based powder mixtures, containing 2 wt% CuO as sintering aid and Sb2O3 in amounts from 0 to 4 wt% as activator of the electrical conductivity, were sintered to high density at temperatures in the range 1000-1400 degreesC and soaking times from 1 to 6 h. Densification behaviour and microstructure development are strongly dependent on the presence of CuO, that gives rise to a liquid phase, and on Sb2O3 that retards the liquid phase formation and hinders grain growth. Cu and Sb cations can enter s.s. in the SnO2 network with different oxidation states and in different positions, depending on the sintering conditions. The characteristics of the grain boundary phase, of the SnO2 solid solutions and their modification depending on thermal treatments were analyzed. The electrical resistivity values varied in a wide range from 10(-1) to 10(4) Omegacm, depending on starting composition and processing conditions: in terms of the final density and of the electrical conductivity, the optimal sintering conditions were found to be 1200 degreesC, for 1-3 h. The electrical resistivity was related to the microstructural features, particularly to the characteristics of the resulting SnO2-based solid solutions. (C) 2003 Kluwer Academic Publishers.