Adsorption of water by Na montmorillonite (Na MMT) and hydroxy-Al precursor of pillared montmorillonite was measured at constant pressure of water vapour (P_H20 = 3.16 kPa) after treating the samples at 300–900 °C. Na MMT kept its high ability to sorb water even after heating to 600 °C. Al pillared MMT sorbed a significantly lower amount of water after calcination at temperatures higher than 500 °C, when hydrophobic Al_xO_y pillars were formed in the MMT interlayer space. Contraction/expansion of Al pillared MMT interlayers during calcination was minimal.