Abstract: The activated carbon fiber (ACF) was fabricated of natural hollow metaplexis japonica seed hair fiber(Mj-fiber) successfully through dewaxing, activation by phosphoric acid and carbonization process at high temperature. The micromorphology and aggregate structure of the ACF were characterized by SEM、XRD、Roman and BET. The results demonstrate that our as-prepared ACF, with graphite-like microcrystalline and disorder structure, possesses high hollow characteristic and surface morphology of multi-stage pores distribution. The total pore volume and specific surface area of our ACF is 1.357 cm3/g and 1882.003 m2/g, respectively. More importantly, the ACF displays excellent absorbility of methylene blue dye molecules in solution. The sorption processes of our ACF follow the pseudo-second-order kinetic equation and the adsorption isotherm conforms to the Langmuir model. The physical absorption dominates, and the theoretical maximum adsorption capacity can reach up to 947.372 mg/g. Furthermore, the adsorption Gibbs free energy △G0<0 and the adsorption enthalpy change △H0>0, obtained from the results of thermodynamic analysis, indicating the absorption behavior is a spontaneous process and positively correlated with temperature. In addition, the effects of pH and electrolyte concentration on the adsorption properties of ACF were analyzed systematically.