We have demonstrated the prospect of dual-layer polybenzimidazole-polyethersulfone/polyvinylpyrrolidone (PBI-PES/PVP) hollow fiber nanofiltration (NF) membranes in the forward osmosis (FO) process for the enrichment and concentration of pharmaceutical products without denaturing the component of interests. The dual-layer hollow fiber membrane via coextrusion technology has an ultra-thin selective skin around 10 mu m, fully open-cell water channels underneath and a microporous spongelike support structure. The self-charged PBI selective skin has an average pore radius at 0.4 nm with a sharp pore size distribution. Experimental results show that the newly developed dual-layer hollow fiber nanofiltration membrane can achieve a high throughput for lysozyme enrichment and less protein fouling when using it as a FO membrane. In addition, the high divalent salt rejection towards Mg2+ at around 90% of this dual-layer membrane ensures the enriched lysozyme product with high purity and without change and denaturing. (C) 2009 Elsevier B.V. All rights reserved.