It was shown using a cone-plate rotational viscometer that the apparent viscosity of a dilute aqueous solution of sodium hyaluronate decreased gradually during the measurement. Hyaluronic acid (HA) forms a characteristic network by entanglements coupling, so two hypotheses could be postulated from the reduction of viscosity due to shearing stress. One was that disentanglement of the temporary network occurred, and the other was that scission of HA chains was responsible. In this study, the reason for the reduction in viscosity was clarified using high-performance gel permeation chromatography with low-angle laser light scattering. It was thus demonstrated that chain scission occurred during the viscometric measurement. On the assumption that the HA. degradation was caused by shearing stress, the effects of shearing rate, the initial molecular weight, salt, and polymer concentrations of samples were investigated. High molecular weight HA chains were preferably severed. From the change in polydispersity of the samples it was inferred that due to the viscoelasticity of HA. solution scission behavior would differ, depending on the shearing rate. Also, the salt and polymer concentrations were found to exert large influences on the degradation. Thus, it was concluded that the scission rate was related to the expansion of HA molecules in solution.