Internal friction peaks resulting from sodium ion diffusion in three kinds of soda glasses have been observed in the temperature range 100° to 200°C for transverse and torsional frequencies between 20 to 400 cps. The heat of activation for sodium ion diffusion was found to range between 17 000–21 000 cal/mole and might probably be slightly dependent on the sodium content. The results obtained were confirmed by electrical resistivity measurements. For quartz glass and for soda glass having Na2O content less than 4 percent, the internal friction peak of the type discussed here could not be noticed, thus indicating that below a minimum Na2O content of about 4 percent, ionic sodium diffusion does not contribute to the anelastic behavior.