PAN based activated carbon fibers which were used for environmental filter were evaluated their pore structure using Hg porosimeter and SEM analysis. Micro and meso pores below 10 nm were uniformly distributed on the fiber surface and the total specific surface area was 1,565 m2/g. From methylene blue(MB) adsorption test, almost adsorption was finished at the early stage around 10 minutes and efficiency was affected by temperature condition. Micro/meso-pores act as adsorption site which the adsorbent was fully filled the pores during adsorption and made some bubble like morphology on the pore site.