Well-crystallized samples of the phyllosilicate magadiite have been synthesized in their sodic form, both purely silicic and with an Al/Si ratio of 30. They have been delaminated by a procedure consisting of CTMA+ swelling in the presence of TPAOH, sonication, and calcination at 700°C to remove the organics, and characterized by XRD, 27Al and 29Si NMR, IR, TEM and SEM, and N2 physisorption after the successive steps of this procedure. The final delaminated solids, consisting of crumpled sheets, exhibit a high (500-510 m2/g), mostly external surface area. While 29Si NMR indicated some loss of structural order, IR suggested the preservation of a typical feature of the magadiite sheets, namely 5-membered (TO4) rings. The acidity of the delaminated Al-containing material was evaluated by low-temperature CO adsorption. This technique revealed strong Brönsted acidic centers, whose behavior was similar to that of Si-OH-Al bridging hydroxyls in pentasil zeolites. Finally, the catalytic activity was evaluated for the test reaction of cumene cracking, and shown to be much higher than that of a reference silica alumina. These results make delaminated magadiite an attractive candidate for use as a novel acid catalyst or catalytic support.