Abstract: Refluxing chromium (III) acetate with a Na⁺-montmorillonite suspension gives rise to the intercalation of linear Cr(III) polyhydroxo-acetate oligomers. Thermally stable chromia pillared montmorillonite materials are obtained upon calcination under ammonia up to 625°C, and basal expansions up to 6 Å are maintained. The porous materials retain high surface areas (366–464 m² g⁻¹), a micropore volume of 0.1 cm³ g⁻¹ and narrow pore size distributions centered between 7.5 and 12 Å. The most thermally stable materials in air were those prepared under ammonia at 625°C, containing NH₄⁺ as the exchangeable ion.