The biological role of chitosan which was prepared by chemical method from shrimp waste Penaeus semisulcatus and the outer skeleton for marine crab Portunus pelagicus in some industrial and agricultural applications were studied. The concentration of prepared chitosan was 1% (w/v) at pH (4 and 8) for 12 hours in precipitation and chelating heavy metals (Lead, Zinc, Iron, Cupper and Cadmium) from of sewage water. Concentration of elements was measured by Flame Atomic Absorption Spectrophotometer ) FAAS). The results of the study indicated that the concentration of the water elements was high before treated with chitosan. The results showed a significant (p<0.05) decrease in element concentration percentage after treated with crab chitosan. In contrast, shrimp chitosan displayed a minimum effect on decreasing the amount of heavy metals. Moreover, the results showed that the higher percentage for mineral adsorption was at pH (4 as compared with 8). The results confirmed the possibility of using chitosan in chelate and precipitate the mineral ions from polluted water.