Abstract: The invention relates to a process for the preparation of bismuth germanate of formula Bi.sub.4 Ge.sub.3 O.sub.12.According to this process, into an aqueous solution is introduced a bismuth compound such as Bi(NO.sub.3).sub.3, 5H.sub.2 O and a germanium compound such as GeO.sub.2, which are respectively able to release into the solution soluble bismuth complexes and soluble germanium complexes. The pH and temperature of the solution in the stability range of the Bi.sub.4 Ge.sub.3 O.sub.12 phase are then brought to value such that there is a simultaneous release of soluble bismuth and germanium complexes and they are reacted to form a precipitate of Bi.sub.4 Ge.sub.3 O.sub.12. The pH is generally approximately 0.5 to 5 and the temperature is below 120.degree. C.