Abstract Adsorption of gallic acid by activated carbons from aqueous solutions has been studied. Activated carbons were prepared from agricultural by-products and Spanish lignites. All carbon series were characterized by N 2 and CO 2 adsorption, mercury porosimetry, and water density. The adsorption processes have been carried out under both static and dynamic conditions. Adsorption isotherms obtained at 298 K were fitted by the Langmuir's equation. In the case of dynamic adsorption some characteristics of the beds, such as breakthrough volume, adsorption capacity at different breakthrough values, and height of the mass transfer zone, were calculated from the breakthrough curves, which were obtained by pumping a solution of the acids through the beds at a constant rate. Adsorption capacity was related to the pore volume of the activated carbons accessible to water. When other electrolytes were present in the gallic acid solutions, the adsorption capacity was enhanced and the rate of the adsorption process was lowered.