A single-step approach for the synthesis of polyphosphazenes containing sulfonic acid functionalities is developed. Polyphosphazene "sulfonation" is conducted via the direct replacement of chlorine atoms of the macromolecular precursor, poly(dichlorophosphazene), PDCP with a sulfonic acid containing nucleophile-hydroxybenzenesulfonic acid. The method makes use of "noncovalent" protection of the sulfonic acid functionality with a hydrophobic ammonium ion, such as the dimethyldipalmitylammonium ion, which then can be easily removed after the completion of the reaction. H-1, P-31, and C-13 NMR and size-exclusion HPLC studies revealed no macromolecular byproducts or noticeable degradation of the polyphosphazene backbone under the conditions of the synthesis. Both sulfonated polyphosphazene homopolymers and mixed substituent copolymers containing 4-ethylphenoxy side groups were synthesized and characterized.