The effect of pH on hydrogen production from liquid swine manure supplemented with glucose by a mixed culture of fermentative bacteria in an anaerobic sequencing batch reactor was evaluated in this study. At 37 +/- 1 A degrees C, five pH values ranging from 4.7 to 5.9 at an increment of 0.3 were tested at a hydraulic retention time (HRT) of 16 h. The results showed that at this HRT, the optimal pH for hydrogen production was 5.0, under which the biogas comprised 33.57 A +/- 5.65% of hydrogen with a production rate of 8.88 A +/- 2.94 L-H-2/day and a yield of 1.48 A +/- 0.49 L-H-2/L liquid swine manure. The highest biomass concentration, highest butyric acid to acetic acid ratio, lowest propionic acid concentration, and the best stability were all found at pH 5.0, while the highest CH4 productivity was found at pH 5.9. For efficient hydrogen production, oxygen content should be controlled under 2%, beyond which an inverse linear relationship (R (2) = 0.986) was observed.