Ultrasonic-assisted simultaneous saccharification and fermentation (SSF) of modified organosolv pretreated oil palm fronds (OPFs) for sustainable production of bioethanol was investigated for the first time in this study. Ultrasound application in industrial processes is able to reduce the process temperature and time, which eventually improves the energy utilization for sustainable production. According to this study, the ultrasonic-assisted SSF of pretreated OPFs was found to improve the bioethanol yield significantly at shorter times compared to the SSF processes without ultrasound. Optimization of the ultrasonic- assisted SSF process resulted in maximal bioethanol concentration (18.2 g/l) and yield (57.0%) at optimum SSF time (5 h), temperature (40 degrees C), pH (5.0), yeast concentration (15 g/l) and solid loading (10% (w/v)). SSF coupled with ultrasound was found as a sustainable way of producing high bioethanol titre from organosolv/H2O2 pretreated OPFs. (C) 2013 Elsevier Ltd. All rights reserved.