The adsorption of acid brilliant blue onto thermally activated coir pith carbon in aqueous solution was studied in a batch system with respect to contact time, pH, and temperature. Acidic pH was favorable for the adsorption of this dye. The surface characterization of thermally activated coir pith carbon was performed using the FTIR technique. Kinetic studies showed that the adsorption of dye on coir pith carbon was a gradual process. Lagergren-first-order, second-order, intra-particle diffusion model and Bangham were used to fit the experimental data. Equilibrium isotherms were analysed by Langmuir, Freundlich, Dubinin-Radushkevich and Tempkin isotherms. The adsorption capacity was found to be 15.24 mg/g by Langmuir isotherm. The pH effect and desorption studies suggest that chemisorption might be the major mode of the adsorption process. The change is entropy (Delta S degrees) and heat of adsorption (Delta H degrees) of coir pith carbon was estimated as 185.45 J/(molK) and 48.02 kJ/mol, respectively. The high negative value of change in Gibbs free energy indicates the feasible and spontaneous nature of adsorption on acid brilliant blue on coir pith carbon. (C) 2007 Elsevier B.V. All rights reserved.