An intermittent-flow, stirred tank reactor (IFSTR) was used to produce biohydrogen from textile wastewater (TW) by activated sludge. The IFSTR was operated at pH 5.5 under various feeding frequencies and TW concentrations. The first intermittent peak biogas production rate of 17.5 L biogas/L-d and HPR of 10 L H2/L-d were obtained at feeding frequency of 12 times/d with TW concentration of 33.1 g hexoses/L. Butyrate and acetate were the major soluble metabolites at peak HPR, whereas lactate and ethanol accumulation decreased the HPR. Close resemblance of bacterial communities in periods of peak HPR with hydrogen producer Clostridium butyricum was observed.