One step pyrolysis/activation of fine powder and fiber from anthracene oil-based pitch in ammonia atmosphere was successfully applied for producing microporous nitrogen enriched carbons. In the process, the preoxidized precursor was heat-treated in ammonia flow at 2 K/min to the final temperature in the range of 300-900 degrees C with 0.5 h soak. The intensive reaction of pitch powder with ammonia at 750-800 degrees C results in N uptake of similar to 10 wt.% and generation of micropores of mean width 0.53-0.67 nm and very narrow pore size distribution (PSD). XPS analysis shows mostly pyridinic nitrogen. Not only increasing process temperature induces enhancement of micropore surface area (S-micro) to 900 m(2) g(-1) but also widening PSD and reduction of nitrogen content. Similar behavior is observed on the ammonia activation of pitch fibers. The advantage of using fibrous precursor is a higher nitrogen uptake (12 wt.%) which can be combined with S-micro of 880 m(2) g(-1) and narrow PSD around 0.8 nm. The ammonia activation of stabilized pitch fibers seems to be a feasible route for producing nitrogen enriched microporous activated carbon fibers of narrow PSD and controllable pore width. (C) 2013 Elsevier B.V. All rights reserved.