This paper presents the results from 92 cycles of an anaerobic sequencing batch biofilm reactor containing biomass immobilized on inert support (mineral coal) applied for the treatment of an industrial wastewater containing high sulfate concentration. The pilot-scale reactor, with a total volume of 1.2 m 3 , was operated at sulfate loading rates ranging from 0.15 to 1.90 kgSO 4 2− /cycle (48 h — cycle) corresponding to sulfate concentrations of 0.25 to 3.0 gSO 4 2− l − 1 . Domestic sewage and ethanol were utilized as electron donors for sulfate reduction. Influent sulfate concentrations were increased in order to evaluate the minimum COD/ sulfate ratio at which high reactor performance could be maintained. The mean sulfate removal efficiency remained between the range of 88 to 92% at several sulfate concentrations. Temporal profiles along the 48 h cycles were carried out under stable operation at sulfate concentrations of 1.0, 2.0 and 3.0 gSO 4 2− l − 1 . Sulfate removal reached 99% for cycle times of 15, 25, and 30 h, and the effluents sulfate concentrations were lower than 8 mgSO 4 2− l − 1 . The results demonstrate the potential applicability of the anaerobic configuration for the biological treatment of sulfate-rich wastewaters.