A 3-year survey on sulfate-reducing bacteria (SRB) was conducted in the waters of the arsenic-rich acid mine drainage (AMD) located at Carnoulès (France) to determine the influence of environmental parameters on their community structure. The source (S5 station) exhibited most extreme conditions with pH lowering to ~1.2; iron, sulfate, and arsenic concentrations reaching 6843, 29 593, and 638 mg L-1, respectively. The conditions were less extreme at the downstream stations S1 (pH ~3.7; iron, sulfate, and arsenic concentrations of 1114, 4207, and 167 mg L-1, respectively) and COWG (pH ~3.4; iron, sulfate, and arsenic concentrations of 854, 3134, and 110 mg L-1, respectively). SRB community structures were characterized by terminal restriction fragment length polymorphism and library analyses based on dsrAB genes. The predominant dsrAB sequences detected were most similar to the family Desulfobulbaceae. Additionally, certain phylotypes could be related to spatio-temporal fluctuations of pH, iron, and arsenic species. For example, Desulfohalobiaceae-related sequences were detected at the most acidic sample (pH 1.4) with high iron and arsenic concentrations (6379 and 524 mg L-1, respectively). New dsrAB sequences, with no isolated representatives, were found exclusively in COWG. This study gives new insights on SRB community dynamics in AMD systems..