The quantitative relationship between sulfate reducing bacteria (SRB) and hydrogen (H<SUB>2</SUB>) production from sulfate (SO<SUB>4</SUB><SUP>2-</SUP>) and ferrous [Fe(II)] enriched wastewater was investigated. Both Fe(II) (0-11,600 mg/L) and SO<SUB>4</SUB><SUP>2-</SUP> (0-20,000 mg/L) improved the H<SUB>2</SUB> production efficiency from wastewater. The H<SUB>2</SUB> yields were increased up to 1.9 mol H<SUB>2</SUB>/mol glucose in 580-1750 mg Fe(II)/L and 1000-3000 mg SO<SUB>4</SUB><SUP>2-</SUP>/L enriched wastewater at pH 5.8-6.2. Quantitative Fluorescence In Situ Hybridization (FISH) analyses revealed that the specific sulfate reducing activities (SSRA) were increased from 0.08 and 0.06 to 0.16 and 0.21 g TS/g SRB h in response to variations in sulfate concentration from 300-20,000 mg/L at pH 5.8 and 6.2, respectively. H<SUB>2</SUB> production was not influenced by low SSRA (@?0.1 g TS/g SRB h), which was independent of pH variation. The results demonstrated that the SSRA and Fe(II) concentration can significantly influence on the biological H<SUB>2</SUB> production from SO<SUB>4</SUB><SUP>2-</SUP> and Fe(II) containing wastewater.