Solutions containing hydroxy-SiAl (HSA) oligocations were prepared by two procedures: 1) treatment of a mixture of orthosilicic acid and AlCl3 with aqueous NaOH, followed by ageing of the product; and 2) preparation and ageing of hydroxy-Al13 oligocations followed by reaction of the latter with orthosilicic acid. Ion exchange of Na,Ca-montmorillonite with HSA oligocations yielded pillared, cross-linked montmorillonites (designated as HSA-CLM) showing a maximum d(001) value of 19.5 A for air-dried samples, and maximum surface areas of approx 500 m2/g after outgassing at 250oC/10-3 torr. Corresponding ion exchange of Li-fluorhectorite yielded HSA fluorhectorites (HSA- CLFH) showing a maximum d(001) value of 19.0 A and a surface area of 355 m2/g. Calculated structural formulae for the HSA-CLM and HSA-CLFH products, based on elemental analysis, showed a gradual increase in the Si/Al ratio in the intercalated HSA oligocations with increasing Si/Al ratio in the pillaring solution. Optimum d(001) values and surface areas of HSA-CLM and HSA-CLFH products were obtained using method 2 and applying a ratio of 1.6-2.5 mmole (Si)Al/g smectite. HSA-CLFH products showed the unusual behaviour of increase of d(001) with increase in T from 400o to 500oC, and essential constancy of d(001) from 500o to 600oC. The HSA-CLM products showed a gradual decrease in surface area, whereas the HSA-CLFH products prepared with a Si/Al ratio of 1.04-2.18 in the pillaring solution showed constant surface areas with increasing T from 250o to 600oC.