A synthetic wastewater with high CONCENTRATION of SULFATE and COD was treated in anaerobic baffled reactor (ABR) coupled with an activated sludge. The work was accomplished in two phases .In the first phase, the CONCENTRATION of SULFATE was kept constant at 500 mg/l, but COD CONCENTRATION was increased from (3000 mg/l to 6000 mg/l), consequently, COD and SULFATE removal in ABR was reached to 80% and 95%, respectively. Some of produced sulfide in ABR converted to sulfur by photosynthetic bacteria which appeared on the top of the ABR. Effluent from the ABR entered to activated sludge where COD removal reached to 60%, but some of sulfide converted to SULFATE. In the second phase, at constant CONCENTRATION of COD, when SULFATE CONCENTRATION was increased from 500 mg/l to 1750 mg/l by steps about 250 mg/l, inhibition was not observed. When effluent of this second phase was entered in activated sludge, COD removal was decreased, and sulfide cause bulking in activated sludge. The ABR and activated sludge were worked with hydraulic retention time (HRT) about 24 hours and 15 hours, respectively. The temperature of ABR system was maintained at 35?C.