In the present work, alkali-treated sewage sludge (SS) was used as a seeding source for H-2 fermentation of food waste leachate (FWL). The role of alkaline treatment of SS was to suppress the activity of non-H-2-producers in SS and also to enhance the solubility of SS. The effect of pretreatment pH and FWL:SS ratio on H-2 production was crucial, by changing the pH conditions and selecting the dominant species. High pretreatment pH and high SS content resulted in high initial pH conditions. The highest H-2 yield of 2.1 mol H-2/mol hexose(added) was achieved at pretreatment pH 10 and a mixing ratio of FWL:SS = 3:5. At these conditions, the initial pH was 7.9, and cultivation pH was maintained within the reported optimum range of 5.5-6.5 during fermentation. It was found that pretreatment pH 9 was not strong enough to suppress the activity of non-H-2-producers in SS, in particular, lactic acid bacteria (LAB). Microbial analysis results confirmed that LAB such as Lactobacillus sp. and Enterococcus sp. were the dominant species at pretreatment pH 9 while Clostridium sp., the main anaerobic H-2-producers, were dominant at pretreatment pH 10. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.