Bench scale anaerobic expanded bed reactors were operated at the U.S. EPA Test and Evaluation Facility to determine the effect of relative concentrations between organics and sulfate on the organics removal. The bench scale results showed that less organics were removed as the sulfate loading rate was increased under the constant organic loading operation. When the organic loading rate was increased, on the other hand, the sulfate removal was increased and reached a plateau value under the constant sulfate loading operation. The former indicated that excessive amounts of sulfate in the influent can affect the anaerobic treatment process adversely, while the latter indicated that the sulfate removal rate can be limited by the organics and sulfate concentration in the influent.