Chitosan, was obtained from red lobster shells (Pleuroncodes monodon). The M̄v of chitosan prepared was 54.000 g/mol with a deacetylation degree of 80%. The retention capacity of chitosan for copper and mercury ions was studied. The adsorption isotherms of Cu(II) and Hg(II) and the mixture of ions are discussed using the Langmuir and Freundlich model. The selectivity from the mixture of both ions was measured. The pH effect on retention was tested. Furthermore, the uptake of both ions in a mixture was compared using chitosan and a commercial resin Amberlite IRA-68.