Hexacyanoferrate(II) and hexacyanoferrate(III) hydrotalcites have been synthesized by exchange of originally existing carbonate ions at pH = 4.5. The samples have been characterized by elemental chemical analysis, powder X-ray diffraction, FT-IR and X-ray absorption spectroscopies, nitrogen adsorption for specific surface area and porosity assessment, and their thermal stability has been characterized by Differential Thermal Analysis and Thermogravimetric Analysis. it has been found that during exchange hexacyanoferrate(II) is partially oxidized to hexacyanoferrate(III), a constant oxidation percentage being already attained after 3 h stirring during synthesis. Hexacyanoferrate(III) ions, however, are partially reduced during the same preparation process, but the reduction degree increases with the stirring time. Decomposition takes place in three consecutive partially overlapped steps : dehydration, decomposition of the interlayer cyanide ligands and dehydroxylation of the brucite-like layers. Upon calcination at 600 degrees C, a mixture of an Al-MgO solid solution is formed, together with MgFe2O4 spinel.