A novel halochromic fiber was synthesized by first aminating commercially available polyacrylonitrile fiber with ethylenediamine and then immobilizing phenolphthalein covalently through a Mannich reaction. The fiber was characterized by XRD, SEM, FTIR and UV-vis spectroscopy. The halochromic properties, response speed and durability of this functional fiber have been investigated. This halochromic fiber exhibited remarkable color change from pale yellow to violet in a wide range of alkaline solutions (pH > 10.1) with short response time (<1 s for 20 wt-% NaOH) and strong recycle stability (>300 times). (C) 2009 Elsevier Ltd. All rights reserved.