The effects of heat-shock conditions on the characteristics of fermentation using granular sludge were examined., The granular sludge was obtained from the wastewater treatment plant of a brewery factory. The temperature and time of heat-shock treatment were changed in the ranges of 60-90 degrees C and 0-60 min. The pH at heat-shock treatment was varied from 3 to 10. Glucose was used as the substrate. The yield and selectivity of hydrogen for the heat-shocked granular sludge were much higher than those for the non heat-shocked granular sludge. In the present fermentation, the optimum conditions of heat-shock treatment for granular sludge were 70 degrees C, 30 min and pH of 6. The hydrogen yield for the second heat-shocked granular sludge was lower than that for the first heat-shocked granular sludge. It was found that a relatively long period for the spore formation before the heat-shock treatment was needed to enhance the hydrogen yield.