The viscoelasticity of the hydrogels, the moisture sorption, and the characteristics of the sorbed water of highly water-absorptive hydroxyethylcellulose (HEC) graft copolymers [e.g., HEC graft copolymers containing partially hydrolyzed polyacrylamide (HEC-P-Hyd-PAM), etc.] were investigated in comparison with commercial absorbents. The viscosity (eta) and the rigidity (G) of the dispersions of their hydrogels were, respectively, proportional to the second to the sixth powers and the fifth to the seventh powers of their concentrations (eta = KC2-6 and G = K’C5-7). With respect to the characteristics of the sorbed water, the conductivity of 0.1 N KCl in the hydrogels of the HEC water absorbents was about 11.8 mS/cm, which was almost the same as that of 0.1 N KCl in pure water, and the water absorbency of dry matter (soybean seeds) in their hydrogels was almost the same as that in pure water. These results suggest that most of the sorbed water in the HEC super water absorbents behaves like free water. The maximum volume of sorbed moisture in a monolayer fashion (V(m)) of HEC-P-Hyd-PAM analyzed using the Brunauer-Emmett-Teller equation was about 0.21 g/g (1.2 mol water/polymer repeat unit), and there was no cluster water at 92% relative humidity or below as a result of applying the cluster function concept.