The present study put an emphasis on the handling of mercury waste by using modified chitosan which obtained from shrimp shell as waste of frozen shrimp. The main aim of the study was to find out the effectiveness of cysteine as modifier to chitosan and its application for adsorption of mercury metal at water bodies. The characterisation study of adsorbent, chitosan-cysteine was done using FT-IR and SEM-EDX, wheres maximum adsorption limit was determined by AAS. The effects of parameters like pH, contact time, maximum adsoption capacity was studied at isothermal condition, on the adsorption process under study. Mechanism of adsorption process was studied according to adsoption kinetic model based under pseudo-first order and pseudo-second order, wheres adsorption isothermal was determined based on Langmuir and Freundlich isotherms. The results of the study indicate that the increase of cysteine amount in the synthetic process has no significant effect on the acquisition of % yield. Adsorption of synthetic results were determined with FTIR, SEMEDX. The optimum condition of metal ion Hg (II) adsorption by chitosan-cysteine at pH 5.5 with time of adsorption four hours. Kinetics model of adsorption follows pseudo-second order. Data on isothermal adsorption follows Langmuir isothermal model with maximum adsorption capacity to metal ion Hg (II) is 4.99 mmol/g, higher than that of earlier results that is 2.41 m mol g