Montmorillonite (Mt) was silylated with 3-aminopropyltriethoxysilane (APTES) in a mixture of water/ethanol medium. The swelling property of the silylated product was evaluated by intercalating of cetyltrimethylammonium bromide (CTAB). Locking effect was observed in the process of silylation. The grafted silane molecules fix the interlayer height of the silylated Mt to a certain value by simultaneous condensation with the two adjacent layers. The locking effect results in the loss of swelling property of silylated Mt and only limited amount of surfactants are able to enter the galleries of the silylated products. The success of the surfactant intercalation suggests that the silylated Mt could be a carrier for the organic target matters. (c) 2012 Elsevier B.V. All rights reserved.