The adsorption capacity of an adsorbent depends on its surface area, pore size, pore-size distribution, and pore volume. The activated carbon produced in a fluidized-bed reactor using coconut shells' was characterized in terms of the pore-size distribution, micropore volume, external surface area, and average pore size. The effects of various parameters, viz., reaction time, fluidizing velocity, particle size, and temperature of activation, using steam and CO2 as activating gases on the above-mentioned characteristics of activated carbon were evaluated. The reaction time, temperature, and fluidizing conditions showed significant effects on the pore-size distribution, pore volume, and average pore diameter. Activating gases also had considerable effects on the characteristics of activated carbon produced in a fluidized-bed reactor.