The morphology and structure of hydrous montmorillonite in different swelling condition have been observed with the aid of hydrophilic ionic liquid (IL; 1-Butyl-3-methylimidazolium Tetrafluoroborate) using electron microscope. The observation mechanism of hydrous montmorillonite with layer structure using IL was revealed by swelling behavior as measured by X-ray diffraction (XRD) and transmission electron microscopy (TEM) with selected area electron diffraction pattern (SAED). The morphology of hydrous montmorillonite containing a large amount of water was also successfully observed by field emission electron microscope (FE-SEM). In addition, the inductively coupled plasma (ICP) and thermogravimetric - differential thermal analysis (TG-DTA) results showed the ion-exchange behavior of hydrous montmorillonite during the IL treatment. The technique allowed the exact morphology to be observed of hydrated materials with layer structure in civil engineering, cosmetics, medical and agricultural fields. (C) 2013 Elsevier B.V. All rights reserved.