The red seaweed, Gelidium amansii, contains proteins such as R-phycoerythrin and R-phycocyanin, as well as polysaccharides. Initial protein extraction from G. amansii yielded 53 mu g/g R-phycoerythrin and 56 mu/g R-phycocyanin. After protein extraction, monosaccharides were produced using hyper thermal acid hydrolysis and enzymatic saccharification. Acetone-butanol-ethanol (ABE) was produced by Clostridium acetobutylicum KCTC 1790. To overcome the different pH requirements for monosaccharide consumption and solvent production, a two-stage pH control culture strategy was developed. Fermentation at pH 6.0 supported a high cell growth rate and both glucose and galactose were consumed completely. The pH was then shifted from 6.0 to 4.5 to produce ABE after 84 h. The maximum ABE concentration reached 15.5 g/L in comparison to 3.1 g/L under fermentation without pH control. The two-stage pH control strategy is a suitable method for ABE production from G. amansii.