Summary: The synthesis of novel methacrylic phosphonated surface‐active monomer by an original method is described. The crucial stage is the telomerization of undec‐10‐enyl acetate with dialkyl (alkyl = methyl or ethyl) hydrogenphosphonate. The phosphonated acetate obtained is selectively hydrolysed to give dialkyl(11‐hydroxyundecyl)phosphonate as a precursor. The alcohol function allows setting of methacrylic side, which is highly reactive in radical polymerization. Particularly, by mono‐dealkylation of dimethyl phosphonate in a selective and quantitative way, the potassium iodide permits to get, at one stage, the expected salt of sodium methyl phosphonate. The new surface‐active sodium methyl(11‐methacryloyloxyundecyl)phosphonate is characterized by 1H and 31P NMR. Its critical micelle concentration evaluated by conductometry is 2.4 × 10−2 mol · l−1.Synthesis of dialkyl(11‐methacryloyloxyundecyl)phosphonate (DAHP) without protection of alcohol function.imageSynthesis of dialkyl(11‐methacryloyloxyundecyl)phosphonate (DAHP) without protection of alcohol function.