Poly-ferric-aluminum-silicate-sulfate (PFASS) with various (Al + Fe)/Si molar ratios was prepared from fly ash to evaluate their coagulation efficiencies in oily wastewater, and the structure and morphology of which were characterized by infrared spectra (FTIR), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Therefore, the results indicate that 16:1 (Al + Fe)/Si mole ratio is beneficial to forming of Si-O-Al and Si-O-Fe bonds, PFASS consists of NaAl(SO4)(2)center dot(H2O)(6) and other crystals, the morphology of PFASS is largely influenced by (Al + Fe)/Si molar ratio, and when the (Al + Fe)/Si mole ratio is 14:1 or 12:1, a chain-net structure with three dimensions appears. Moreover, the coagulation experiment results show that the removals of turbidity and COD from oily wastewater are affected by coagulant dosage and (Al + Fe)/Si mole ratio of PFASS. Too much or too little PFASS is not conducive to the coagulant efficiency, and the optimal (Al + Fe)/Si mole ratio is 12:1 for the turbidity removal and 16:1 for COD removal. Nevertheless, when the dosages of PFASS reach the effective coagulation levels in the oily wastewater. COD are not reduced along with turbidity removal. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.