OXI-PAN fibers, Kynol fibers, and rayon fibers were used as precursors for the preparation of activated carbon fibers (ACFs) by chemical activation with KOH at 800 degrees C. The effects of different precursor fibers and fiber/KOH ratios on the final ACFs are discussed. The precursor fibers used were appropriate for the ACFs in a single stage pyrolysis process. The OXI-PAN fibers, which were activated with KOH of 2.0M, showed a specific surface area of 2328 m(2)/g, however, lost the fiber shape because of low yields. The Kynol fibers and Rayon fibers showed the high yields, but lower specific surface areas of 900m(2)/g and 774m(2)/g, respectively, at KOH of 1.5M. The OXI-PAN fibers, which were activated with KOH of 1.5M, have a specific surface area of 1028m(2)/g and higher micro-pore volumes and lower yields rather than Kynol-1.5 and Rayon-1.5 samples. This phenomenon is attributed to higher chemical resistance of the Kynol and Rayon fibers rather than OXI-PAN fibers. However, the Kynol fibers were the best precursors on KOH activation at 800 degrees C when carbon yields, surface areas, and micropore volumes are condisered.