Effects of pH（pH 3.0, 5.0 and 8.0）on mechanism of selenite uptake by rice roots were studied using excised roots of rice seedlings. Results indicate that in solutions of pH 3.0 and pH 8.0, 0.10 m moll^-1 DNP, 1.0 m molL^-1NaF and low temperature (4°C) could only inhibit selenite uptake to a small extent, and selenite uptake varied with selenite concentration, showing a linear curve. However, pH 5.0 inhibited uptake of most selenites, showing a saturation curve. Further study revealed that both HgCl₂ and AgNO₃inhibited uptake of most selenites at pH 3.0, while anion channel inhibitors did that of a few at pH 8.0. Apparently, selenites infiltrated into roots actively at pH 5.0 and was absorbed passively by the roots at pH 3.0 and pH 8.0. Furthermore, selenites were absorbed into the roots through aquaporins at pH 3.0 but absorbed into the roots via other routes than anion channels at pH 8.0.