We have carried out single crystal X-ray diffraction measurements of (Bi 2 O 3 ) 0 . 7 5 (Gd 2 O 3 ) 0 . 2 5 in the temperature range between 123 and 292 K. The structure was refined by the least-squares method, using about 70 reflections. The structure is very similar to that of δ-Bi 2 O 3 and it was concluded that the oxygen ions are statistically located towards the cations ascribing to relatively short Gd-O bond distance. The decrease of the ionic conductivity is mainly due to the difference between electronegativities of Bi-O and Gd-O bonding.