Entanglement network of carboxymethyl cellulose (CMC) was characterized based on the dynamic viscoelasticity of the concentrated solutions in an ionic liquid. According to the concentration dependence of the molecular weight between entanglements (M (e)), M (e) for the molten state (M (e,melt)) for CMC was estimated to be 3.9 x 10(3) as a chain variable reflecting the chemical structure of the polysaccharide. Furthermore, relations between M (e,melt) and other chain variables were examined to elucidate the specificity in the entanglement properties of CMC and related polysaccharides. It was shown that the number of entanglement strands (P (e)), the ratio of the cube of the tube diameter, and the volume occupied by the entanglement strand, for CMC was 72 being significantly larger than the universal value of ca. 20 recognized for flexible polymers. Anomalous values of P (e) > 20 were also obtained for related polysaccharides such as cellulose and amylose.