PURPOSE: To produce an adsorbent for heavy metal ions which has excellent selective adsorption power for mercury ions by depositing cysteinyl groups or peptide groups on an amimo group contg. resin contg. primary amino groups.

CONSTITUTION: This adsorbent consists of the amino group contg. resin wherein at least a part of the N-position is substituted by the cysteinyl groups or the peptide groups expressed by the general formula H(Cys-Gly-Gly)n (the Cys in the formula is a cysteinylgroup, Gly is a glycyl group, n is 1W6 integers). There are linear high polymer compds. such as aminated polystyrene and the like or cross-linked high polymer compds. such as aminated polystyrene-divinyl benzene copolymer as the amino group contg. resin used as a carrier. The primary amino group is contained at about 0.01W100 millimole with respect to 1g these high polymer compds., after which the above-mentioned substituent is incorporated into the carrier resin.