Deposition of hyperbranched poly(acrylic acid) (PAA) films on porous supports is an attractive method for synthesizing derivatizable, ultrathin composite membrane skins. We previously synthesized these films by sputtering a thin gold layer onto a porous alumina support and then grafting several layers of PAA to a self-assembled monolayer of mercaptoundecanoic acid on the gold. This paper demonstrates grafting of PAA onto PAA/poly(allylamine hydrochloride) (PAH) films that were prepared by alternating polyelectrolyte deposition. This procedure overcomes the inconvenience associated with sputtering of gold and allows synthesis of defect-free membranes using only one grafted PAA layer. Membrane skins consisting of 2.5 bilayers of PAA/PAH plus 1 layer of grafted PAA (total thickness of similar to 14 nm) effectively cover the underlying pores of porous alumina supports without filling them, as shown by field-emission scanning electron microscopy (FESEM) images. When derivatized with H2NCH2(CF2)(6)CF3, these composite membranes show an ideal selectivity of 2.4 for O-2 over N-2, demonstrating the absence of defects in this system. The chemistry developed for the grafting process also allows modest derivatization of PAA/PAH films with H2NCH2(CF2)(6)CF3 to increase hydrophobicity.