Adsorption of naphthenic acids has been studied on commercial weak and strong anion-exchange resins. The capacity and equilibrium constant of adsorption on these resins are compared with those obtained with zeolites, bentonite and polyvinyl pyridine. Macroporous weakly anionic ion-exchange resins with weak tertiary amine group have good adsorption capacity for the removal of naphthenic acids from petroleum oil as compared to strong anion-exchange resins with isoporous structure although the strong anion-exchange resin shows greater interaction with naphthenic acids. The rate of uptake of naphthenic acid is governed by the internal diffusional resistance which is also dependent on adsorbed phase concentration.