The separation and extraction of a phenolic compound called p-nitrophenol were studied by aqueous two-phase systems (ATPS). Solubility data were experimentally obtained at ambient temperature using dipotassium hydrogen phosphate, diammonium hydrogen phosphate, and sodium dihydrogen phosphate and polyethylene glycol polymers with molecular weights of 1000 and 4000 g/mol. The tie-lines were also obtained for solvation data. Then, experimental results were correlated with thermodynamic model UNIQUAC. Factors affecting the binodal curves such as salt types and temperature were also investigated. The salting-out ability of salts was studied, and the results showed that dipotassium hydrogen phosphate had the best result. By examining the effect of three temperatures of 298.15, 305.15, and 313.15 K on p-nitrophenol extraction, the percentage of extraction decreased by 6.05%. The percentage of p-nitrophenol extraction decreased with increasing molecular weight of the polymer and increased with increasing the polymer concentration. The highest obtained percentage of extraction was 96.85% in ATPS including dipotassium hydrogen phosphate (30% w/w) and polyethylene glycol 1000 (40% w/w).