Bio-H2 production from food waste of 10% total solid (TS) using anaerobic mixed microflora under thermophilic condition was operated at different hydraulic retention times (HRTs) of 1.0, 1.26, 1.9 and 3.8 days. The system was configured to produce H2 gas in conjugation with COD and nitrogen removal in a continuous stirred tank reactor (CSTR). The pH in H2 reactor was maintained at a range of 5.0 ~ 5.6 with circulation of supernatant from denitrification tank by circulation pump. The objective of this study was to investigate the influence of HRTs on continuous H2 production from a high-solid food waste in fed-batch operation of CSTR. The results obtained are as follows: Maximum H2 production rate (5.1 l/l d) was achieved at the HRT 1.26d, which gave H2 content of 55% and H2 yield of 3.1 mol H2/mol hexose. Continuous H2 production was achieved for over 30 days at each HRT. Only little amount of CH4 at HRT 3.8d was observed. Total carbohydrate and TS removal efficiencies in H2 reactor were 89 ~ 98% and 60~77% at each HRT. Acetate and butyrate as major volatile fatty acid (VFA) were produced throughout experimental conditions. This result suggests that stable H2 production from high-solid food waste could be achieved at a range of pH 5.0 ~ 5.6 by circulating supernatant from denitrification tank without using chemical reagent.