In this study, we investigated the nano-platelet structures of original and organically modified montmorillonite clays. Atomic force microscope observation gave accurate width and thickness of the nano-platelet clays. The organically modified clays could not be homogeneously dispersed even in organic solvent. Ultrasonication of the solution resulted in the destruction of the layered structure of the clays. In contrast, the supernatant solution before ultrasonication contained the mono-layered nano-platelets of the organically modified clays whose surface was rough in the angstrom level due to the adsorbed molecules.