This work presents the effect of acid-pretreatment on H-2 fermentation of food waste with detailed microbial information by next generation sequencing. The pretreated food waste at pH 1.0-4.0 was cultivated under mesophilic conditions without external inoculum addition. From the food waste acid-pretreated at pH 1-3, H-2 yields in the range of 1.37-1.74 mol H-2/mol hexose(added) were achieved, attaining the highest value at pH 2. Clostridium sp. such as Clostridium acetobutylicum ATCC 824 and Clostridium perfringens occupied more than 70% of total number of sequences at pH 1-3. On the other hand, in the control (no pretreatment) and at pH 4, lactic acid bacteria such as Lactobacillus and Streptococcus were found to be the dominant genus (>90% of total number of sequences), resulting in a low H-2 yield. In addition, the effect of substrate concentration on H-2 fermentation was investigated, and the maximum H-2 productivity was estimated to be 27.2 L H-2/L/d by Andrew's model. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.