The temperature dependence of N-2 adsorption isotherms on carbon micropores having different pore widths was measured in the temperature range 77-207 K and was simulated using the grand canonical Monte Carlo (GCMC) technique. The adsorbed amount decreased with increasing temperature, irrespective of the difference in the pore width. However, the adsorption decrease depended on both pore width and temperature. The narrower the pore width, the less the adsorption decrease. A slight increase in the measuring temperature from 77 to 82 K gave rise to a large decrease in the adsorption for activated carbon fiber having an average pore width of 1.1 nm, whereas carbon samples with 0.6-0.7 nm average pore width did not show such a remarkable difference. Molecular fluctuation in pores of width 1.2 nm increased as the temperature was increased in the GCMC simulation.