ZnO,Nb2O5 and ZnO-Nb2O5 doped tin dioxide based ceramics prepared by the pressureless sintering have been investigated as function of sintering character and electrical property.The microstructure and the phase constitution was measured by scanning electrical microscope and XRD.The results indicate that ZnO can improve the volume density of the materials,but cannot decrease the electrical resistivity signally,the optimal content of ZnO was 0.5wt%-0.75wt%;Nb2O5 can signally decrease the electrical resistivit...