Abstract: The stability constant of the complex UO2ReO4+ is measured to be 0. 41±0 .07 (μ=1.0mol/l)with solvent extraction of uranyl ion by HDNNS(dinonyl naphthalene sulfonic acid) -heptane from an aqueous solution of perrhenate indifferent concentrations. The result of this work can be used for the estimation of the strength in the cornplexation between pertechnetate and uranyl ions, since pertechnetate and perrhenate are chemical analogs.