A series of composite flocculants PFC-PD with different basicity (B) of polyferric chloride (PFC), different weight percentage (w(P)) and intrinsic viscosity (eta) of polydimethyl diallylammonium chloride (PDMDAAC) were prepared by prepolymerization. The turbidity, dissolved organic carbon (DOC) and specific ultraviolet absorbance (SUVA) removal efficiency as well as flocculation mechanism of PFC-PD were compared with that of PFC, PDMDAAC and Successive addition of PFC and PDMDAAC in treating high DOC and high alkalinity surface water by jar tests. The effect of B, w(P) and eta on coagulation efficiency and mechanisms were also studied. The experimental results showed that PFC-PD was more efficient and more applicable for turbidity, DOC and SUVA removal than PFC, PDMDAAC and successive addition of PFC and PDMDAAC. Further, the water pH was slightly depressed by PFC-PD. Coagulation efficiency of PFC-PD was improved at lower B, larger w(P) and larger eta. Charge neutralization was dominant mechanism of PFC-PD. (C) 2008 Elsevier B.V. All rights reserved.