Hydroxyaluminium and hydroxychromium pillared montmorillonites were prepared by intercalation and subsequent calcination of Ca-montmorillonite separated from Jelsový Potok bentonite (Central Slovakia). Ca-montmorillonite and pillared clays were studied by thermal and X-ray diffraction methods. Nitrogen adsorption-absorption data were used to determine pore size distribution, specific surface area, volume of micropores and surface of mesopores. Isomerization of o-xylene to p- and m-xylene, and o-xylene disproportionation were used to test the catalytic activity of investigated materials. The measurements showed increasing catalytic activity in the order Ca-montmorillonite<chromium pillared montmorillonite<aluminium pillared montmorillonite. The results confirmed that increasing surface area had a positive effect on the conversion and disproportionation of o-xylene.