Alginic acid derived from macroalgae was evaluated as a renewable biomass feedstock for the hydrothermal production of furfural over Amberlyst-15 as a solid acid catalyst. The maximum yield of furfural (18.5 mol%) was attained when 0.5 wt% of alginic acid was hydrothermally treated with 600 mg of Amberlyst-15 at 180 degrees C for 30 min. Although the production of furfural over the catalyst was enhanced with increasing temperature and reaction time, elongated time-on-stream gave rise to the decrease in the yield of furfural due to the generation of humin originating from the side reactions of furfural. Higher catalyst loading resulted in the increased furfural production, however, the acid-catalyzed polymerization of furfural with other organic products was simultaneously accelerated with increasing the catalyst amount, leading to the decrease in the overall yield of furfural. Amberlyst-15 showed considerable catalytic performance in the production of furfural from alginic acid and it could be reused 5 times without significant deactivation. (C) 2016 Elsevier B.V. All rights reserved.