In this study, Ascophyllum nodosum was studied as a biomass for ethanol production. A. nodosum was degraded to monosaccharide by hyper-thermal (HT) acid hydrolysis and enzymatic saccharification and analyzed using response surface methodology (RSM) and the Michaelis-Menten equation. Maximum monosaccharide concentrations of 20.3 g/L glucose and 7.0 g/L mannitol were obtained from HT acid hydrolysis and enzymatic saccharification from 8%(w/v) of A. nodosum. Fermentation was conducted using Pichia stipitis and P. angophorae adapted to high mannitol concentrations. Neither non-adapted P. stipitis and P. angophorae nor adapted P. stipitis could ferment all mannitol in the A. nodosum hydrolysate. Adapted P. angophorae produced the highest ethanol concentration among various yeasts, with ethanol production reaching 13.6 g/L with an ethanol yield (Y) of 0.50. Optimization of HT acid hydrolysis and enzymatic saccharification, in combination with the use of adapted yeast, could enhance overall A. nodosum ethanol fermentation yields.