A novel approach to preparation of composite asymmetric nanofiltration membranes is reported based on a thin selective layer deposited by electropolymerization (EP) on top of an asymmetrically porous and electronically conductive porous support. Support films with ultrafiltration characteristics were cast from a concentrated dispersion of carbon black particles, a few tens of nanometers large, in a solution of polysulfone followed by precipitation in a non-solvent bath (phase inversion). Composite membranes with poly(phenylene oxide) and polyaniline thin top layers were prepared by EP deposition from solutions of phenol and aniline, respectively, of which polyaniline film demonstrated a dense uniform structure and water flux and rejection to sucrose and magnesium sulfate in the nanofiltration range.