The effect of initial pH from 5.0 to 9.0 on H(2) fermentation of food waste was investigated. In this batch experiment, however, unlike previous studies for initial pH, operational pH was maintained at 5.0 by the addition of alkaline solution. Although the period for pH drop from the initial values to 5.0 was less than one-tenth of the entire fermentation, this short period significantly affected the H(2) production performance. At initial pH 6.0-9.0, successful H(2) yield of 1.3-1.9 mol H(2)/mol hexose(added) was achieved with a peak value at pH 8.0. The H(2) yield achieved at initial pH 8.0 was corresponded to the 8.13% of total energy content in the substrate. At initial pH 5.0, the smallest butyrate production, but the highest ethanol production was detected, indicating unfavorable conditions for H(2) production. There was no significant relationship between total required amount of alkaline solution and initial pH values. (C) 2011 Elsevier Ltd. All rights reserved.