Activated carbon fibres are new adsorbents, which seem very promising for air or water treatment. In this work, rayon fibres which have been carbonized and activated in the form of woven cloths, are studied by means of two kinds of microscopy: Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The resulting observations show the effect of carbonization and activation on the fibre surface structure. The influence of activation conditions (oxidation gas, temperature and duration) is studied and confirmed by N2 adsorption. The specific porosity properties of fibres are then used to adsorb different organic compounds in aqueous solutions, with low molecular weights (aromatics like phenol) and high molecular weights (humic substances). A good correlation is found between these adsorption data and the microscopic observations.