In this study, laboratory model experiments on the interactions of Cr with natural ecological restoration substances were carried out to estimate optimum conditions for the reduction of Cr in soils and/or waters. For natural ecological restoration substances, humic substances (humic acid and fulvic acid) and clay minerals (bentonite and imogolite) were used. The experiments, performed at pH 4-8, yielded the following results: (1) Cr(VI) was reduced to Cr(III) by the humic substances; moreover, the reduction ability of the humic substances decreased with increasing pH. (2) The complexation of Cr(III) proceeded faster than the reduction of Cr(VI) and reached a maximum at pH 5. (3) Cr(III) was best removed at pH 4 and 5 by bentonite, but the removal ratio decreased with increasing pH. Furthermore, the removal effect of bentonite decreased with the addition of a humic substance. (4) While Cr(VI) was never removed by bentonite, the removal was slightly improved by the addition of a humic substance and an increase in pH. (5) An effect of imogolite on the removal of Cr(VI) was observed at pH 4 and 5. Reaching a maximum at pH 4, the effect was not indicated at pH 6-8.