The removal of organic pollutant from aqueous solution was carried out by using modified activated carbon surface. Activated carbon was modified using chemical and physical treatment, such as using oxidizing agent (HNO₃) and air oxidation, respectively. In this study, Rhodamine B was used as the organic pollutant. The results showed that activated carbon modified with air oxidation treatment rapidly attained the Rhodamine B adsorption after 30 minutes of contact time. Adsorption data are used for modelling, from the pseudo-first-order and pseudo-second-order kinetic equation and intra-particle diffusion models. The isotherm adsorption of Rhodamine B was fitted with Freundlich isotherm indicating that adsorption occurs on a heterogeneous surface through a multilayer adsorption mechanism. In addition, the intra-particle diffusion suggests that there were two stage mechanisms which contributed to the adsorption efficiency of Rhodamine B.