Cadmium (Cd) pollution in soils has become a serious environmental problem as this toxic metal may be easily absorbed by plants, leading to inhibition of plant growth and development.Rice is a global staple food crop, however, its quality may be threatened by the accumulation of Cd in grain.The risk to human health associated with Cd-tainted rice may be reduced by minimizing the Cd mobility from soil to rice root.So far, a large number of studies investigated the effects of soil pH, Eh and root iron plaque on Cd bioavailability.These factors may increase, decrease or have no effect on the Cd uptake by rice.However, the underlying mechanisms for these various effects still need further clarification.Thus, in this study, effects of pH (4.5-7.5), Fe and Cd concentrations on Fe and Cd adsorption in the rhizosphere and on the root surfaces of rice were studied using nutrient solution and vermiculite culture.The results showed that Eh and pH in rice rhizosphere differed among various treatments, and the oxidizing potential was lower at 0.9mg/L Cd than at 0.5mg/L Cd, while the acidity in the rhizosphere at 50 mg/L Fe was higher than at 30 mg/L Fe.Besides, the composition and amount of Fe/Cd on the rice root were controlled by the pH and Eh in the rhizosphere.The adsorbed Fe and Cd were lowest at pH 6.0 and respectively reached the maximum values at pH 4.5 and 7.5.However, the mechanisms of Fe/Cd adsorption on the rice root surface were different from those on the surfaces of vermiculite.On the vermiculite surfaces, crystallized Fe was the major form, accounting for 73% to 78% of total Fe adsorption, while on the rice root, noncrystalline Fe was the major form, accounting for 91% to 95%, both of which separately had significant relations with the treatment pH and Eh (crystallized Fe on the vermiculite surfaces: p_pH=0.011, p_Eh =0.042; noncrystalline Fe on the root surfaces: p_pH=0.050, p_Eh =0.004).Either EXC-Fe or EXC-Cd on vermiculite surfaces had significant relations with treatment pH and Eh (pH: p_Fe<0.001, p_Cd=0.009; Eh: p_Fe=0.016, p_Cd=0.002), while EXC-Fe and EXC-Cd on the surfaces of rice root just significantly correlated with pH (p_Fe=0.007, p_Cd=0.048).In addition, Fe and Cd treatments affected the adsorption of these two elements on the rice root.Compared with control, Cd addition decreased Eh and increased pH in the rhizosphere, leading to a decline of soluble Cd and a rise of Cd adsorbed on the root surfaces, while Fe application increased Eh and decreased pH in the rhizosphere, resulting in more soluble Fe/Cd and less adsorption of the two elements on the rice root surface.These were physiological reactions of rice to the stresses caused by excessive Fe and Cd.