To investigate the effect of dissolved organic matter (DOM) on the adsorption of phenanthrene (PHE) by montmorillonite (MMT), organic clay complex was prepared by associating montmorillonite with DOM extracted from landfill leachate. Both the raw MMT, DOM. and MMT complex (DOM-MMT) were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photo-emission spectroscopy (XPS), and scanning electron microscope (SEM). Batch adsorption studies were carried out on the adsorption of PHE as a function of contact time, temperature, and adsorbent dose. The sorption of PHE on complex was rapid, and the kinetics could be described well by the Pseudo-first-order model (R(2) > 0.99), with an equilibrium time of 120 min. The adsorption isotherm was in good agreement with the Henry equation and Freundlich equation. Also, thermodynamic studies showed that the adsorption process was exothermic and spontaneous in nature. Compared with MMT, the adsorption capacity of DOM-MMT complex for PHE was greatly enhanced. The effects of DOM on PHE sorption by MMT may be attributed to the changes in the surface structure, the specific surface area, the hydrophobic property, and the average pore size of MMT. A series of atomistic simulations were performed to capture the structural and functional qualities observed experimentally. (C) 2011 Elsevier Inc. All rights reserved.