gamma-Alumina is widely employed as catalyst support in catalytic hydrogenation of polycyclic aromatic hydrocarbons (PAHs) due to its excellent surface properties. Despite the extensive work effort in improving the catalytic performance of active ingredient, the molecular fundamental studies of the interaction between PAHs and support surfaces are still limited. In this work, the adsorption of naphthalene, anthracene, and phenanthrene on two types of hydroxylated gamma-Al2O3 (110) surfaces with different hydroxyl concentration (5.9 and 8.9 OH/nm(2)) were systematically investigated by DFT method with GGA (PBE) functional. It was found that the size and structure of molecules could greatly affect the adsorption behavior. The order of adsorption energies of PAHs on two types of surfaces was: anthracene > phenanthrene > naphthalene, indicating that the adsorption of larger and linear aromatic is more exothermic. Furthermore, comparison of the results before and after the dispersion correction showed that dispersion interaction played a crucial role in stabilizing PAHs, and was dominant for the poor hydroxylated surface. Conformation of PAHs by using PBE and PBE-D models demonstrated that the inclusion of dispersion forces the molecules closer to the surface in order to maximize the dispersive interaction. The results reported herein emphasize the significance of dispersive interaction, which is beneficial to the design of efficient gamma-Al2O3 support for hydrotreatment.