Several lignin-based activated carbon fibers (ACFs) were prepared by initial synthesis of lignin-phenol-formaldehyde (LPF) resins with varied lignin contents, 8-20%, respectively, and then the melt spinning and thermal treatments. Because the guaiacyl groups of lignin reacted with the formaldehyde, the role of lignin played becomes a dominator for controlling the thermal properties of LPF resin and the pore size and related properties of ACFs. This was proven by the comparison of the scanning electron microscope photographs of all prepared ACFs. FTIR spectra showed that the ACFs were structured by lignin-contributed carbons. The porosity and adsorption behavior of these ACFs were also studied and compared. Results showed that the ACFs with 14% lignin content have better pore structure and adsorption properties. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 989-994, 2011