In the present contribution, the synthesis of well‐defined water‐soluble phosphonic‐acid based poly(2‐ethyl‐2‐oxazoline) and the preliminary study of their sorption properties were reported. For such purpose, poly(2‐ethyl‐2‐oxazoline) (POx) was first prepared. Then, controlled hydrolysis allowed the obtaining of statistical poly(2‐ethyl‐2‐oxazoline)‐stat‐poly(ethyleneimine) (POx‐st‐PEI) with 20% of ethyleneimine units, which allowed maintaining water solubility of the copolymers. The latter were successfully functionalized with either dimethyl(acryloyloxymethyl) phosphonate (APC1) or diethyl‐2‐(acrylamido)ethylphosphonate (DAAmEP) using Michael reaction. Phosphonated esters were hydrolyzed to produce phosphonic acid groups, thus, leading to hPOx‐st‐PEI‐APC1 and hPOx‐st‐PEI‐DAAmEP copolymers. Finally, functionalized statistical copolymers were successfully used for the sorption of divalent or trivalent metallic cations. The reported work aims at reporting the synthesis of original polyoxazoline materials functionalized with phosphonic acid groups that could be further employed for water treatment in polymer enhanced ultrafiltration processes.