Organic solvent usually was used in a polymer-based membrane fabricating process. In this study, otherwise pure water was utilized to prepare the polymer composite membrane. A pure aqueous emulsion was firstly prepared through directly dissolving a commercially available amphiphilic hyperbranched polymer (HBP), Bottom W3000 into water. As the cross-linking agent, glutaraldehyde, glycol, triethylamine, or tetraethyl orthosilicate was then added into the emulsion, respectively. Finally, the HBP was self-assembled onto the surface of polyacrylonitrile (PAN) ultrafiltration membrane by immersing the PAN substrate into the emulsion to form the composite membrane. The homogeneous dispersion of the HBP in the emulsion was confirmed by transmission electron microscopy, and the formation of the composite membrane was characterized by IR spectra, field emission scanning election microscopy and atomic force microscopy. Importantly, the composite membrane performed an excellent separation performance in dye retention and desalination. For example, with the operation pressure of 0.5 MPa, the retention of methyl blue could reach 97.0% with a flux of 55.0 L m(-2) h(-1), while the salt retention was lower than 12.0%. This work thus not only illustrated a new approach for the preparation of nanofiltration membrane in aqueous solution, but also produced a potentially useful polymer-based composite membrane for highly efficient dye desalination. (C) 2013 Elsevier B.V. All rights reserved.