The low-frequency electrical conductivity of xanthan in salt-free aqueous solutions has been measured in a wide temperature range, from 5 to 70 degrees C, covering the interval where a thermal-induced conformational transition in the polymer chain occurs. The polymer concentration has been varied up to 10 mg/mL, from the semidilute region, where polymer chains are partially entangled with each other, to the concentrated region. Deviations from the dilute regime and the conformation of the polyion in a double-stranded helix with a finite radius make the counterion condensation of the Manning model for highly charged polyelectrolytes inapplicable. On the other hand, on the basis of the present conductivity data and of our previous measurements of radiowave dielectric relaxations of the same polymer solution (J. Phys. Chem. 1995, 99, 274) we find that a fraction of counterions, although different from that predicted by Manning, will condense, altering the value of the conductivity of the whole solution. This condensation is largely independent of the polymer chain structure and, to a first approximation, of polyion concentration, the fraction of free counterions assuming a value that increases with temperature from about f = 0.53 at 20 degrees C to about f = 0.75 at 70 degrees C. With these values and considering an appropriate conductivity expression consisting of additive contributions, i.e., polyion and free counterions, according to the suggestions of the Manning theory, a reasonable agreement with the experimental data can be found.