Abstract: Polyphosphonatester salts PPAand PPB (2400<M<3700) containing 5-fluo-rouracil in the main chain have been studied by improved Bruss rnenbranc osmometer and dynamic osmomctry, viscometry, conductivity method. It was indicated from experiment, that the molecular conductance of infinite dilution ∧₀ of the samples in DMSOis small, so normal osmotic pressure behavior were observed. The number average molecular weight M_n and second virial coefficient A₂ wene obtained. Dissolving them in pure water or in methanol, the condition, ∧₀ of PPBthe samples become large and the solutions exhibit properties of polyelectrolyle solution. But at high dilutions, both curves of η_SP/C-Cand ∧₀-Cappear anomaly.