PURPOSE: To obtain an absorbent of high ability of metallic element absorption by dissolving condensation type tannin powder into ammonia water, and then by producing a gel composition by mixing an aldehyde water solution with the solution above, and by maturing the gel composition at room temperature or stabilizing it through heating.

CONSTITUTION: Condensation type tannin powder is dissolved into ammonia water and then aldehyde water solution is added and mixed with the ammonia water solotion to produce a gel composition. Mixing rates of the tannin powder, the ammonia and the aldehyde are, against a total amount, within a range of 3 to 35wt.% for the tannin powder, 33 to 35wt.% for the ammonia and 30 to 62wt.% for the aldehyde, for instance. Subsequently, the gel composition is leaving and matured at room temperature of 20 to 25°C for 3 to 4 days, or is stabilized for rather short period by heating it. By this treatment, an absorbent of which absorptivity for uranium, thorium, uranium in sea water and various kinds of metallic elements is very high, can be obtained.