Dark brown forest soil was treated with radioactive aqueous solution of ⁷⁵SeO₃ at rate of 0.131 ppm and 1.631 ppm.Wheat was planted on the soil contained Se of 0.023 ppm and 0.493 ppm respectely.After the wheat being havested,residual ⁷⁵Se in the soil was fractioned by various extractants.Various forms ⁷⁵Se in the soil were in the order of isotopically exchangeable Se>that extracted by NH₄OH>extracted by HCl>that water soluble>that extracted by K₂SO₄·⁷⁵Se in the soil was present mainly as the form exchanged by NaHSeO₃.This fraction of Se constituted 28% of the total Se in soil,that extracted by NH,OH 20%;that soluble in water,6-7%.Most of ⁷⁵Se being in the form of SeO₃^2- added to the soil was quickly adsorbed by the soil.The results of the experiments also indicated that more than 90% of soluble Se was transformed into insoluble forms including organic Se and inorganic Se in the form of the SeO₃^2- In addition,the SeO₃^2- may also be reduced to Se⁰ and Selenides.Thus the availability of Se for plants was reduced.Content of Se in wheat have a directly correlated to that in the soil.It is suggested that to raise soluble Se in the soil is an important practice for increasing Se in wheat.