Several samples of activated carbon (AC), previously outgassed and treated with H2SO4 solutions of varying concentration, were prepared. The contact between the phases and the outgassing of AC were carried out under controlled conditions. The chemical composition and the thermal behaviour as well as the texture of the samples were studied. Techniques used were chemical analysis, FT-IR spectroscopy, thermogravimetric analysis, gas adsorption, mercury porosimetry and density measurements. After the contact of H,SO, solutions with AC, the mass of samples increased greatly. It was associated with the uptake by AC of components of the solution, especially H2SO4. The presence in the samples of HSO4- and SO42- ions was shown by the FT-IR spectra. The mass increase was strongly dependent on the method of preparation of the samples. In the heat treatment of the samples between 30 and 800 degrees C a great mass loss occurred below 400 degrees C. However, it was small at higher temperatures and when the samples were outgassed at 120 degrees C for 12 h, at 133x10(-3) Pa. The introduction of H2SO4 solution in AC pores produced a drastic reduction in the surface area and in the microporosity of the material. It also affected the pore-size distribution in the mesopore and macropore ranges.