Catalytic characteristics of activated carbon manufactured from palm shell (ACPS) for methane decomposition was studied using a thermobalance by measuring thee mass gain with time. A reaction order of 0.5 is obtained for methane decomposition over the activated carbon and the activation energy is 210 KJ mol(-1). The activity of the activated carbon had decreased in almost a linear relationship with the amount of carbon deposited at 800 degrees C, which indicates that the carbon deposition occurred uniformly on to the carbon surface, while diffusion effect appeared to occur significantly at the last stage of the process at reaction temperatures up to 950 degrees C. The study of mass gain using different particle sizes indicates the existence of mass transfer effect and the pore mouth blocking which seem to take place particularly in large particles. Comparison between ACPS and commercial based activated carbon (AC) shows almost similar values with regard to change of mass gain with time, maximum amount of carbon deposited before deactivation and the deactivation time. (C) 2009 Published by Elsevier B.V.