Succinoglycan samples ranging in weight-average molecular weight from 1.0 x 10(5) to 8.7 x 10(6) (in 0.1 M aqueous NaCl at 25 degrees C), prepared by ultrasonication of a native sample (Rheozan), followed by fractionation, were investigated by static light scattering, sedimentation equilibrium, and viscometry in 0.1 M aqueous NaCl at 25 degrees C where the polysaccharide assumes a certain ordered (helical) conformation. The measured radii of gyration and intrinsic viscosities showed the polysaccharide to behave like a semirigid chain in the aqueous salt. Their analysis based on the unperturbed wormlike chain yielded about 1500 nm-1 and 50 nm for the linear mass density and the persistence length, respectively. The former value was almost twice that expected for the single succinoglycan molecule, and thus it was concluded that the predominant molecular species of succinoglycan present in the aqueous salt is a double helix or an aggregate composed of paired single helices.