Concentration dependence of radius of gyration (R-g) of sodium poly(styrenesulfonate)s (NaPSS) in aqueous solutions without added salt was studied by small-angle neutron scattering measurements over a wide range of concentration. The R-g values are always higher than those of corresponding nonionic polymer, polystyrene, and the concentration (C) dependence of R-g of NaPSS in the semidilute region (C < 0.3 x 10(3) kg/m(3)) can be well expressed by the scaling relation (R-g proportional to C-1/4), while R-g values in the concentrated region are almost constant at the value almost equal to that at Theta condition. The crossover concentration from the semidilute to concentrated regions was also consistent with our previous studies of viscoelastic properties of polyelectrolyte solutions without added salts.