The equilibrium molalities In3+ in {In2(SO4)3+Na2SO4+HDEHMTPCA+n-C8H18+water} were measured at ionic strength from (0.1 to 2.0) mol脗脗kg脗脗脗1 containing Na2SO4 as supporting electrolyte in aqueous phase and at constant molality extractant at temperatures from (278.15 to 303.15) K in organic phase. The standard extraction constants K0 at various temperatures were obtained by methods of extrapolation and polynomial approximation. Thermodynamic quantities for the extraction process were calculated.