Poly(vinyl phosphonic acid) (PVPA) as obtained by free radical polymerization of aqueous vinyl phosphonic acid was studied by light scattering (SLS, DLS) and size exclusion chromatography (SEC) in dilute aqueous solutions containing sufficient salt in order to screen long range electrostatic interactions. Samples of 37<<(M)over bar>(W)<110 x 10(3) were studied. The polymers showed positive A(2)-values in aqueous NaH2PO4 solution (0.04 m), and self-diffusion behavior and R-H/R-G -ratios indicative of the structure of random coiled chains. A comparison of the SEC-elugrams of the PVPA-samples with those of commercially available standards of poly(acrylic acid) sodium salt gave a fit to the same calibration curve described by 109 P-n(PVPA) = -0.21 nu(e) + 7.0(+0.1) which correlates the number average degree of polymerization (Pn) with the elution volume nu(e). This indicates that PVPA and PAA have the same hydrodynamic structure under given solution conditions.