Modified 13X zeolites and active carbons were studied for HCl adsorption from biogas employed as fuel of MCFCs. 13X zeolite was modified by addition of Cu or Zn by ion exchange or impregnation: commercial active carbon was modified by impregnation with KOH, NaOH or Na2CO3 solutions. The materials were tested for HCl adsorption in a laboratory apparatus designed to the scope. The tests were carried out under flow conditions with a 100 ppm HCl/N-2 mixture at T = 40 degrees C and atmospheric pressure. Breakthrough curves were obtained from potentiometric analysis of HCl in the stream effluent from the adsorption cell. The zeolites modified by ion exchange were more effective for HCl adsorption than those modified by impregnation. The active carbon modified with Na2CO3 solution showed the highest adsorption capacity of 3.3 x 10(-4) mol HCl g(-1) at breakthrough concentration of 1 ppm. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.