The removal of Acid Red 398 (AR398) dye from dye-containing solution using coagulation/flocculation process with polyaluminum chloride (PAC) and Alum was investigated. The effect of different parameters involving pH, dosage of coagulant, initial dye concentration, and bentonite as a natural coagulant aid was examined. According to the obtained results, the optimum pH, at which the maximum removal occurred, was about 4 and 5 for PAC and Alum, respectively. However, PAC performed efficient in a broader pH range. In the case of PAC, the best removal efficiency was about 80% for the dosage of 100-120 mg/l,while, it was about 60% for 140-160 mg/l of Alum. With the increase of initial dye concentration in the range of 25-250 mg/l, the removal efficiency for both coagulants increased at first (from 25-100 mg/L) and then declined. Bentonite, as a coagulant aid, slightly enhanced the removal efficiency. By adding 20 mg/l of bentonite, the efficiency increased by 15% and 9% for Alum and PAC, respectively.