Ammonium polyphosphate was used as a novel activating agent for producing activated carbons (APACs) with well-developed mesoporous structure and high carbon yield from a renewable biomass (Enteromorpha). The influences of activation temperature and chemical impregnation ratio on the carbon yield and porous structure were investigated. APACs were characterized by pore structural analysis and scanning electron microscopy. The results showed that ammonium polyphosphate promoted the development of mesopore at lower temperature (around 600 degrees C) and the average pore diameter concentrated around 37 nm. All the APACs were prepared with high carbon yield (maximum 71%) and high mesopore fraction (>60%). The advantage of the generated mesoporous carbon was demonstrated by the high adsorption capacity for acid brilliant scarlet up to 416.7 mg/g. These results indicated that ammonium polyphosphate holds promise for producing activated carbon with excellent yield and mesoporous structure. (C) 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.