Silver nanoparticles were added into anaerobic batch reactors to enhance acidogenesis and fermentative hydrogen production simultaneously. The effects of silver nanoparticles concentration (0-200 nmol L-1) and inorganic nitrogen concentration (0-4.125 g L-1) on cell growth and hydrogen production were investigated using glucose-fed mixed bacteria dominated by Clostridium butyricum. The tests with silver nanoparticles exhibited much higher H-2 yields than the blank, and the maximum hydrogen yield (2.48 mol/mol glucose) was obtained at the silver concentration of 20 nmol L-1. Presence of silver nanoparticles reduced the yield of ethanol, but increased the yield of acetic acid. The high silver nanoparticles had higher cell biomass production rate. Further study using the alkaline pretreated culture as inoculum was carried out to verify the positive effect of silver nanoparticles on H-2 production. Results demonstrated that silver nanoparticles could not only increase the hydrogen yield, but reduce the lag phase for hydrogen production simultaneously. (C) 2013 Elsevier Ltd. All rights reserved.