BACKGROUND Coagulation/flocculation is widely used in the treatment of dye wastewater because of the low cost, high efficiency, short process and convenient operation. However, with the increase of pollutants in water and in recent years the higher requirement for environment protection, traditional flocculants have found it difficult to meet the processing requirements. Therefore, to develop new, efficient, stable and environment-friendly flocculants is very necessary and urgent. RESULTS Decoloration performance and mechanism, stability and structure of flocculants were determined from experimental data, and the results indicated that chitosan and poly-ferric cerium silicate (CTS-PFCS) flocculant, a three-dimensional chain-net structure with bar-like branches, was a complex compound rather than a simple mixture of raw materials. The decoloration performance and stability of this flocculant was superior to that of poly-ferric cerium silicate (PFCS) when treating Direct Red dye wastewater, and also it had a wide range of pH application. The main mechanism for flocculation is charge-neutralization and chemical adsorption in the initial stage of flocculation and later bridge-aggregation. CONCLUSION A novel inorganic-organic composite flocculant CTS-PFCS was successfully synthesized by the combination of chitosan and homemade PFCS. The potential use of chitosan as an organic additive for modifying inorganic polymers flocculant in the clarification of wastewater was demonstrated. (c) 2018 Society of Chemical Industry