The removal of both anions (phosphate, arsenate, arsenite and borate ions) and cations (copper ions) has been investigated by employing a lab-developed amphoteric polybenzimidazole (PBI) nanofiltration (NF) hollow fiber membrane. The amphoteric characteristics are due to the imidazole group within PBI molecules that makes the PBI NF membrane have an isoelectric point near pH 7.0 and show different charge signs based on the media pH. Investigations on the rejection capability of typical anions, e.g. phosphate, arsenate, arsenite, borate anions and typical heavy metal cations, e.g. copper ions, reveal that the PBI NF membrane exhibits impressive rejection performance for various ions removal. However, their rejections are strongly dependent on the chemical nature of electrolytes, solution pHs and the feed concentrations. The experimental results are analyzed by using the Spiegler-Kedem model with the transport parameters of the reflection coefficient (sigma) and the solute permeability (P). The PBI NF membrane may have potential to be used in industrial removal of various environmentally unfriendly ion species. (C) 2007 Elsevier B.V. All rights reserved.