A white calcium bentonite (CaB) from the Kutahya region/Turkey was activated by heating it for 6 hours at 97degreesC in H2SO4 solution. The mass percentage of H2SO4 in the bentonite-acid mixture was varied from 0 to 70%. The chemical analysis (CA), cation exchange capacity (CEC), differential thermal analysis (DTA) curves and X-ray diffraction (XRD) patterns of the prepared samples were determined. The specific surface area (A) and the specific micropore-mesopore volume (V) were calculated respectively from the adsorption and desorption data of N-2 obtained at liquid N-2 temperature. How the calcium montmorillonite (CaM) layers in the CaB were decomposed during the preservation of the crystal structure is discussed by using CA, CEC, DTA and XRD data. The variations in the porosity of CaB during acid activation were related to the variations in the crystal structure and are discussed. Although the values of A and V were 43 m(2)g(-1) and 0.107cm(3)g(-1) respectively for the original bentonite, these values reached a maximum and were 134 m(2)g(-1) and 0.295 cm(3)g(-1) respectively after activation by 40% H2SO4.