The purpose of this paper is to study the enhancement of Bsi20310 exopolysaccharide (Bsi20310 EPS, secreted by an Antarctic sea-ice bacterium Pseudoalteromonas sp. Bsi20310), on coagulation of reactive brilliant red X-3B (RX-38) by ferric chloride. The effect of solution pH, EPS addition timing and NaCl concentration for coagulation of RX-3B was investigated. The results showed that at pH 10. Fe(III) dosage of 55 mg/L, adding 150 mg/L Bsi20310 EPS enhanced the decolorization effectively. NaCl had little effect on the enhancement of Bsi20310 EPS. The EPS had negative surface charge and could combine with positive Fe(III)-dye flocs to form neutralized settleable Fe(III)-dye-EPS flocs. Results of residual Fe(III) concentration and ferric-ferron reaction kinetics indicated that EPS addition led not only more Fe(III) to participate in coagulation but also to form more Fe-b (the most effective ferric hydrolysis species) in coagulation. Bsi20310 EPS enhanced Fe(III) coagulation performance by neutralization, bridging and sweeping to improve the floc aggregation. (C) 2010 Elsevier B.V. All rights reserved.