Inverse gas chromatography (IGC) was applied to characterize the surface of sepiolite. The adsorption thermodynamic parameters (the standard enthalpy (ΔH 0 ), entropy (ΔS 0 ) and free energy of adsorption (ΔG 0 )), the dispersive component of the surface energy (γ S d ), and the acid/base character of sepiolite surface were estimated by using the retention time of different non-polar and polar probes at infinite dilution region. The specific free energy of adsorption (ΔG sp ), the specific enthalpy of adsorption (ΔH sp ), and the specific entropy of adsorption (ΔS sp ) of polar probes on sepiolite were determined. ΔH sp were correlated with the donor and modified acceptor numbers of the probes to quantify the acidic K A and the basic K D parameters of the sepiolite surface. The values obtained for the parameters K A and K D indicated an acidic character for sepiolite surface. © 2005 Friedr. Vieweg & Sohn/GWV Fachverlage GmbH.