Several compositions of NdYb1-xGdxZr2O7 (0 <= x <= 1 0) ceramics were prepared by pressureless-sintering method at 1973 K for 10h in air The relative density microstructure and electrical conductivity of NdYb1-xGdxZr2O7 ceramics were analyzed by the Archimedes method X-ray diffraction scanning electron microscopy and impedance plots measurements NdYb1-xGdxZr2O7 (0 <= x <= 0 3) ceramics have a single phase of defect fluorite-type structure and NdYb1-xGdxZr2O7 (0 7 <= x <= 1 0) ceramics exhibit a single phase of pyrochlore-type structure however the NdYb0 5Gd0 5Zr2O7 composition shows mixed phases of both defect fluorite-type and pyroch lore-type structures The measured values of the grain conductivity obey the Arrhenius relation The grain conductivity of each composition in NdYb1-xGdxZr2O7 ceramics gradually increases with increasing temperature from 673 to 1173 K. NdYb1-xGdxZr2O7 ceramics are oxide-ion conductor in the oxygen partial pressure range of 1 0 x 10(-4) to 1 0 atm at all test temperature levels The highest grain conductivity value obtained in this work is 1 79 x 10(-2)S cm(-1) at 1173 K for NdYb0 3Gd0 7Zr2O7 composition (C) 2010 Elsevier Ltd All rights reserved