The partitioning behavior of the perchlorate ion on the aqueous two phase system (ATPS) NaNO3 + poly(ethylene glycol) 4000 (PEG 4000) + H2O was studied at T = (288.15, 298.15 and 308.15) K. Two salts with different cation were used, NaClO4 and KClO4. The partition coefficient for the perchlorate ion in the ATPS was investigated as a function of temperature, concentration gradient of the PEG between the phases and perchlorate concentration. It was found that as temperature increases the partition coefficient values increases, similar behaviours were observed when the concentration gradient of PEG increases and when the perchlorate concentration increases. The thermodynamic parameters obtained by the thermodynamic relations show that the transfer of anions from the bottom phase to the top phase is entropic driven and that the partition process is endothermic. In addition, the Chen-NRTL model was applied to correlate the experimental data of the partition coefficients, for this purpose, the Flory-Huggins and Pitzer-Debye-Huckel expressions were used to take into account the entropy of mixing molecules and the long-range electrostatic interactions of the ions, respectively. A good agreement between experimental data and correlated results was obtained. (C) 2016 Elsevier B.V. All rights reserved.