Electrochemical impedance spectroscopy (EIS) was used to study the fouling produced due to the adsorption of poly(vinyl sulfonic acid) on polyethersulfone membrane during metal ion recovery by polymer-enhanced ultrafiltration (PEUF). A solution of PVSA (40 mM in monomeric unit and pH 3.0, 4.5, and 6.0) was placed in a ultrafiltration cell, and then a stream of metal ions (2.0 mM in Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Pb2+) was passed from reservoir to cell. Fouled membranes were studied by EIS at low and intermediate frequencies. Measurements of hydrodynamic permeability and ATR-FTIR spectra were also obtained. Different relaxation processes were observed with characteristic frequencies (f (0)) similar to 78 kHz and f (0) similar to 3562 kHz for active layer and clean membrane, respectively, while the frequencies for the fouled membrane f (0) = similar to 79.4 and f (0) = similar to 2511.9 kHz (pH 3.0). The value of f (0) could not be defined at pH 6.0. The relaxation times obtained were in the order of x10(-5) and x10(-3) s approximately for all cases. Our results suggest that relaxation mechanisms, at intermediate frequencies, can mainly be associated to polarization processes or to the migration of charge carriers.