Separation of copper ions from aqueous solution by nanofiltration was shown to be a feasible process to accomplish an effective copper removal over a broad operational range. Experimental results indicated that the rejection of copper ions increases with increasing the charge valence of co-anions present in aqueous solution. Higher degrees of copper removal were achieved for experiments conducted in acidic solutions than those conducted in alkaline solutions. The copper rejection increased with increasing operating pressure until a limiting rejection was reached, further application of higher pressure did not increase copper rejection. The surfactant presented in aqueous solution was adsorbed by the membrane to form a secondary filtration layer on the membrane surface, therefore, influenced the surface charge characteristic of the membrane. The rejection of copper chelate was markedly influenced by the solution pH and the molecular weight of chelate. The solution-diffusion model combined with film theory adequately described the behavior of copper rejection from aqueous solution by nanofiltration. (C) 2004 Elsevier B.V. All rights reserved.