The flocculation performance of polydiallydimethylammonium chloride (polyDADMAC) coupled with polyacrylamide for treating pulp and paper mill wastewaters was studied. The flocculation performance tests were carried out in jars with polyDADMAC and polyacrylamide (PAM) dosages of 0.4-2.0 mg L-1 and 0.4-8.0 mg L-1, respectively. The tests were conducted at a rapid mixing rate of 200 rpm for 2 min, followed by a slow mixing rate at 30 rpm for 10 min, and settling time of 5 min. Polyacrylamide was introduced into the wastewater samples 45 s after the addition of polyDADMAC. The reduction efficiency of turbidity, chemical oxygen demand (COD) and total suspended solids (TSS) were the main evaluating parameters. It was found that poyDADMAC incorporated with PAM was efficient in treating pulp and paper mills wastewater. Increasing dosages of polyDADMAC increased the destabilization of particles and produced small flocs, while the addition and increasing of PAM increased the size of flocs for a better synergistic flocculation process. (C) 2011 Elsevier B.V. All rights reserved.