Sorption behavior of heavy metal ions by various kerateine gels, whose thiol groups were substituted with different groups, were investigated. For this purpose, the thiol groups of kerateine gels were modified by (i) functional residues with chelate-forming or ion-binding nature, (ii) residues with large group moments, and (iii) non-specific alkyl groups. In acid media, the sorption behavior of Hg2+ by these kerateine gels depended strongly on the substituent introduced, although introduction of any substituent could cause no appreciable increase in the uptake. The results were discussed in relation to the chemical structure of kerateine gels. On the other hand, prominent increases in the Hg2+ uptake were observed for all types of kerateine gels independent of their substituent, when the pH of medium goes from neutral to alkaline. The sorption isotherms of Hg2+ observed at pH 9.0 for S-alkyl kerateine gels were almost the same as that for the thiol-type gel. A series of experiments on Hg2+ desorption from the gel showed that the sorption characteristics of S-substituted kerateine gels were more advantageous than that of the thiol-type gel from the standpoint of recovering Hg2+ once sorbed by the kerateine gel. In addition, it was found that the sorption behavior of some metal ions, i. e., Cd2+, Pb2+, and Cu2+, varied to some extent with the substituents introduced, although all types of kerateine gels exhibited predominantly higher uptakes for Hg2+ than those for these metal ions.