Rheological measurements on a high molecular weight Hyaluronic Acid (from rooster combs) were performed to obtain information on the viscoelastic and temporary network characteristics of Hyaluronic Acid solutions as a function of the concentration. From rheological experiments, the critical concentration c* and the concentration dependency of the plateau modulus G degrees e were determined. Further on, structural parameters as Me, the average molecular weight of the polymer segments between entanglement points, and DN, the average distance between entanglement points, were estimated.