We study the rheological properties of sodium polystyrene sulfonate in salt-free and excess added salt solution. The overlap concentration scales as c* ∝ N –2 (DI water) and c* ∝ N –0.77 (excess salt), corresponding to rodlike and expanded coil conformations, respectively. A comparison of small-angle X-ray scattering and viscosity data reveals that c* in salt-free solution may be quantitatively estimated as the point at which the viscosity of a NaPSS solution is ≃5/3 that of the solvent. The entanglement crossover and entanglement density are found to be approximately independent of the concentration of the added salt, and similar to those of neutral polystyrene in good or θ solvents. These results indicate that polymer conformation has a weaker effect on entanglement formation in solution than expected by packing models of polymer entanglement.