Heavy-metal fixation by the chelating polymers is of great importance in environmental applications. In this work, the molecular mechanism of chromate uptake by dithiocarbamate modified starch (DTCS) was investigated. It was found that the DTCS can achieve a maximum adsorption capacity at pH value of 5.0. In such solution, the adsorption kinetics showed two stages, which involved in different molecular mechanisms. The first was a fast stage. It lasted for about 60 min. In the stage, over 80% of maximum adsorption occurred and a Cr(VI)-DTC ester formed. The ester was stable in the first hour, and then the Cr(VI) reduction took place in the second stage. The reduction of Cr(VI) was coupled with the oxidation of DTC, producing elemental sulfur and sulfonate. The formed Cr(III) still fixed in the oxidized DTCS without lost of adsorption capacity. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012