Abstract: A cellulose-derived sponge showing good flexibility even in a dried state is disclosed, which comprises a matrix of a cellulose having an open-cell structure. The sponge shows mechanical properties satisfying at least one of the following conditions (I) and (II):Y.ltoreq.0.07X.sup.3 +0.39X.sup.2 -0.04X+0.04 (I)Z.ltoreq.0.24X.sup.3 +1.17X.sup.2 -0.78X+0.08 (II)wherein X, Y and Z stand for the thickness (mm), the bending rigidity (gf cm.sup.2 /cm) and the hysteresis of bending moment (gf cm/cm), respectively, of the sponge having a bulk density of 0.8 g/cm.sup.3 or less and a water content of 25% by weight or less. The sponge may be prepared by mixing viscose, reinforcing fibers, salt cake, a foaming agent and an anionic polyelectrolyte with each other, and solidifying the mixture in a mold.