In this study, a novel composite inorganic-organic coagulant was prepared by polyferric chloride (PFC) and polydimethyldiallylammonium chloride (PDMDAAC). The variations of size and specific surface area with respect to pH for composite polyferric chloride-polydimethyldiallylammonium chloride (PFC-PDMDAAC) were investigated, and the coagulation efficiency of PFC-PDMDAAC was studied by jar-test, and Photometric Dispersion Analyzer 2000 (PDA 2000) was used to investigate floc aggregation process of PFC-PDMDAAC. The results show that the average size and specific surface area of PFC-PDMDAAC are larger than that of PFC. The coagulation efficiency of PFC-PDMDAAC is higher than that of PFC and PDMDAAC. The floc aggregation process shows that kaolin particles may be aggregated to micro-flocs by Fe(III) species in PFC-PDMDAAC at first, and then the micro-flocs are bridged together to form large flocs by organic coagulants in PFC-PDMDAAC. The soluble dye is aggregated initially to insoluble dye micro-compound by the reaction of PDMDAAC, and then the insoluble dye micro-compound is aggregated to large flocs by Fe(III) polymers in PFC-PDMDAAC. (c) 2008 Elsevier B.V. All rights reserved.