The percolation of water through waste landfills produces leachates with high ammonium concentrations which can generate ammonium-exchanged clays within geochemical barriers.These leachates also contain several volatile organic compounds (VOCs) that can interact with the clay barrier. The aim of this study was to characterize the sorption of eight shortchain VOCs (acetonitrile, methyl tert-butyl ether, dichloromethane, benzene, phenol, ethanol, acetone, and aniline) on ammonium-smectite, and to identify their sorption mechanisms. The treated samples were characterized by carbon and nitrogen elemental analysis, infrared spectroscopy, powder X-ray diffraction, and thermo-gravimetric analyses. For acetonitrile, methyl tert-butyl ether, dichloromethane, and benzene, no sorption was detected. Phenol, ethanol, and acetone were very weakly sorbed, through Van der Waals interactions. Aniline molecules were strongly sorbed on ammonium-smectite mainly with hydrogen bonds between aniline and interfoliar water molecules. However, aniline sorption decreased the hydrophilic character of the ammonium-smectite, which may increase the permeability of the clay barrier.