A gamma alumina nanofiltration membrane, prepared by a sol-gel process, exhibits interesting properties for the filtration of metallic complexes. Experimental rejection and fluxes depend on the pH of the solution. Comparison of the distribution diagrams of the species in solution as a function of pH, established for several metallic complexes using equilibrium constants, shows that rejections and fluxes are affected by the size and the charge of the complex. High rejection ( > 95%) can be reached if the molecular weight of the complex is higher than 400. For positively charged complexes, the flux of the permeate is almost independent of the pH of the solution, whereas for negatively charged ones, the flux increases with increasing pH.