Activated carbon fibers were prepared from stabilized PAN fibers by physical and chemical activation to compare their characteristics. In this study, stabilized PAN fibers were activated by physical activation with steam and CO$_2$, and by chemical activation with KOH. The fabricated activated carbon fibers were evaluated and compared such as specific surface area, pore size distribution, pore volume, and amount of iodine adsorption. In the steam activation, a specific surface area of 1635 m$^2$/g was obtained after heat treatment at 990$^{circ}C$. Otherwise, in the CO$_2$ activation, produced activated carbon fibers had been a specific surface area of 671 m$^2$/g after heat treatment at 990$^{circ}C$. In chemical activation using KOH, a specific surface area of 3179 m$^2$/g was obtained with a KOH/ stabilized PAN fiber ratio of 1.5 : 1 at 900$^{circ}C$. Nitrogen adsorption isotherms for fabricated activated carbon fibers showed type I and transformation from type I and II in the Brunauer-Deming-Deming-Teller (B.D.D.T) classification. Increasing specific surface area Increased the amount of iodine adsorption in both activation methods. Because the ionic radius of iodine was smaller than the interior micropore size of activated carbon fibers.