In the solvent extraction system {R(3)N + NH(4)ReO(4) + n-C(7)H(16) + HCl + H(2)O}, the equilibrium molalities of ReO(4)(-) were measured at ionic strength from (0.1 to 2.0) mol.kg(-1) in the aqueous phase containing NH(4)Cl as supporting electrolyte in the range of 278.15 K to 303.15 K. The standard extraction constants K(0) at various temperatures were obtained by methods of Debye-Huckel extrapolation and Pitzer polynomial approximation. Thermodynamic properties for the extraction process were calculated.