Abstract: Interaction of La3+ and Ce3+-exchanged hectorites with oligomeric hydroxy-Al cations results in the formation of cross-linked hectorites possessing moderately high surface areas (∼220–280 m2/g) and high thermal stability. The basal spacings of these products were generally in the range 17.0–18.0 Å, the exact d(001) value depending on the age of the hydroxy-Al oligomeric solution and on the pH of the starting hectorite dispersion. Interaction of Li- or Ce-fluorhectorite with hydroxy-Al oligocations produced the corresponding cross-linked fluorhectorites, which showed markedly higher basal spacings (18.2–20.0 Å for air-dried samples), surface areas (∼300–380 m2/g), and thermal stability, as compared with those of the cross-linked hectorites. The cross-linking agent applied in the synthesis of the hydroxy-Al hectorite and fluorhectorite products consisted of a solution of hydroxy-Al oligomers aged for periods of 7 to 27 days. A constant ratio of 2.0 mmole Al/g of smectite was used in all preparations. The high basal spacings and porosity of the newly synthesized products are consistent with a structure similar to that previously proposed for cross-linked hydroxy-Al montmorillonite.