Functional ultrafiltration membranes can be used for water decontamination. Here, we investigate the use of plasma polymerization to modify polymeric membranes with poly(allylamine) in order to filtrate aqueous solutions contaminated with Ni(II) ions. A preliminary study is performed to control growth kinetics of polymer thin films with respect to the energy provided to the precursor during deposition. Filtration experiments then enable to quantify the efficiency of the different functional coatings as for their retention of Ni(II) ions and to identify the optimal characteristics of the polymer thin films. Retention rate as high as 96% can be achieved by this single‐step functionalization process, which is very competitive compared to conventional multi‐step wet chemical functionalization techniques.