The recovery of sulfuric acid from effluents containing metallic salts (Mg, Zn, Mn) was achieved by electrodialysis with a Nafion(R) cation exchange membrane modified in situ by electrodeposition of polyethyleneimine on one side of the membrane. The purity of the acid obtained depends on the experimental conditions of this electrodeposition. The total metal leakage through the modified membrane can be lowered to 0.5% with no significant increase in the energy consumption of the process due to a possible increase of the electrical resistance. These results are comparable with, and even better than, those obtained with commercial membranes specially designed for this type of application. The advantage of this modification process is the possibility of regenerating the surface layer directly in the membrane stack.