In this study some characterization tests of acidic pumice were performed using various techniques such as Mercury Intrusion Porosimetry (MIP). Scanning Electron Microscope (SEM). X-Ray Diffraction (XRD). Thermal Analysis (DTA-TG), FTIR and its electrokinetic properties in water such as zeta potential (ZP), isoelectrical point (IEP), indifferent, specifically adsorbing and potential determining ions were determined The results showed that (i) pore dimensions of the irregular or oval and fibrous cavities of the pumice varied between 0.05 mu m and 2 mm depending on its particle size and these cavities usually did not intersect each other, (n) as the pumice particle size decreases, both total pore volume and total pore surface area significantly decrease as well: (m) pumice maintained its thermal stability approximately tip to 900 degrees C, (iv) pumice had a negative surface charge between pH 1.8 and 114; and (v) Cl-, Br- SO42-, Na+, Al(OH)(2)(4) and Ca2+ ions were indifferent. C16H33(CH3)(3)N+, Al3+ and Al(OH)(2+) cations were specifically adsorbing and, H+ and OH-ions were potential determining ions for acidic pumice (C) 2009 Elsevier B V All rights reserved