【Objective】 Iron plaque on root adsorbs heavy metal elements in the soil, thus reducing the content of heavy metals in the environment the plant grows in, while selenium is antagonistic to heavy metal elements in plant roots, thus inhibiting the transfer of Cd, As, Mn and some other heavy metals in the roots of rice seedlings as was found in the researches. In the presence of a proper amount of iron plaque, selenium reacts with Cd, As, Mn, and so on to form insoluble compounds that accumulate in the iron plaque, thus reducing toxicity of these heavy metals to the plants. In this study, a hydroponic experiment was conducted to explore effects of the iron plaque on the surface of the roots of rice seedlings on absorption and transport of mercury by the plants treated with selenium. 【Method】Having been disinfected and washed clean, rice seeds were sown in Hoagland culture medium for germination. Out of the seedlings, 24 consistent in growth were selected and transplanted into two groups of vessels with Hogland culture medium, one treated without selenium (Se0) and the other with selenium (Se0.5, 0.5 mg L^-1 in the form of Na₂SeO₃), for cultivation for 2 weeks. Then the rice plants were moved into Fe² (FeSO₄)solutions (pH=5.5), 0, 25, 50 and 100 mg L^-1 in concentration, or Treatment Fe0, Fe25, Fe50 and Fe100, separately, for 24 h, to let iron plaque form on root surface. And then the rice plants were then transferred into HgCl₂ solution, 0.3 mg L^-1 in concentration for 72 h of cultivation. Each treatment had three replicates. 【Result】No significant effect of the iron plaque was found on growth of the rice seedlings, but selenium was to be able to increase the plants in biomass. With rising Fe concentration in the solution, iron contents in the shoots and roots of the plants and in the dithionite-citrate-bicarbonate (DCB) solution all increased. The iron content in the DCB solution (extraction of root surface iron plaque) reached 57.3%～96.2%, significantly higher than that (1.1%～17.5%) in the shoot and (2.7%～25.9%) in the root of the rice seedlings, Most of the iron in the seedling plants were accumulated in the iron plaque or DCB extract. With the rising amount of iron plaque on the root surface, the content of mercury in the roots and shoots of the plants decreased significantly. The addition of selenium did not affect much the content of mercury in the shoots and roots of the plants in Treatments Fe0 and Fe25, but it did reduce the content of mercury significantly in Treatments Fe50 and Fe100. With the formation of iron plaque on the root surface, the content of mercury in the shoots and roots reduced because the iron plaque adsorbed much mercury and the addition of Se(Ⅳ) enabled the iron plaque to adsorb more mercury, thus increasing the proportion of mercury in the iron plaque and consequently reducing that in the shoots of the plans. Quite obviously, Se significantly enhances Hg fixation capacity of the iron plaque on the root surface of rice seedlings. 【Conclusion】Under hydroponic conditions, iron deposits on the root surface to form iron plaque, which inhibits Hg adsorption by rice roots and upward transfer of Hg in the plant. With the forming of more iron plaque, Hg fixation capacity of the coating increases significantly, too, thus markedly reducing Hg accumulation in the rice seedling. Se(Ⅳ) can alleviate the effect of mercury stress on rice, inhibit Hg transfer from roots to shoots and reduce Hg accumulation in the shoots, thus playing a role in protecting rice from mercury toxication. This study has certain practical significance in improving the quality of rice in mercury contaminated area and ensuring food safety.