Ion-exchange chromatography (IEC) with the lowest step recovery (< 50%) is still a bottleneck of the essentially four-step chromatographic procedure for the purification of recombinant hepatitis B surface antigen (r-HBsAg) from transformed Chinese hamster ovary (CHO) cell line. The low recovery is mainly resulted from the change of the assemble structure of HBsAg particles such as disassociation or aggregation on the surface of the absorbent during binding and eluting procedures. To improve the chromatographic efficiency of IEC, the influence of ligand density from 0.041 to 0.130 mmol diethylaminoethyl (DEAE)/ml absorbent on IEC of r-HBsAg was investigated. The retention time of HBsAg particles depended highly on ligand density. Higher HBsAg recovery and purification factor (PF) were obtained from the absorbents with lower ligand density. Under the optimum chromatographic conditions, the HBsAg recovery was increased from about 44% to 66% and the PF was increased from 9 to 13 by decreasing the ligand density from 0.130 to 0.041 mmol DEAE/ml absorbent. (c) 2006 Elsevier Ltd. All rights reserved.