Seven kinds of sodium rare earth germanate glasses. (Na2O)(35.7)(RE2O3)(7.2)(GeO2)(57.1) (RE (RE=Sm, Gd, Dy, Y, Ho, Er, and Yb), were prepared, and their properties as a Na+ ionic conductor were compared with those of the previously reported silicate glass analogues, (Na2O3)(35.7)(RE2O3)(7.2)(SiO2)(57.1). Density was increased with increasing the atomic weight of rare earth element. Crystallization temperature for the (Na2O)(35.7)(Sm2O3)(7.2)(GeO2)(57.1) glass was about 600 degrees C, which was about 150 degrees C lower than that of the corresponding (Na2O)(35.7)(Sm2O3)(7.2)(SiO2)(57.1) glass. Conductivities of the Ge system glasses were little affected by the change in ionic radius of the rare earth. The conductivities of the (Na2O)(35.7)(Y2O3)(7.2)(GeO2)(57.1) and (Na2O)(35.7)(Y2O3)(7.2)(SiO2)(57.1) glasses were almost the same, though the covalent bond character between Na+ and oxide ions was found to be weakened in the Ge system from their Na-23 NMR spectra. (C) 2007 Elsevier B.V. All rights reserved.