In this work, the ability of four nanoparticles including Al2O3, TiO2, graphene, and graphene oxide (GO) as additives for extraction of cephalexin in aqueous two-phase systems composed of polyethylene glycol (PEG) and three sodium-based organic salts was investigated. For this purpose, phase diagrams and the liquid liquid equilibrium (LLE) data for the {PEG 6000 + sodium citrate, sodium tartrate, sodium succinate + H2O} and partition coefficient for cephalexin were determined. The addition of 0.001 wt % graphene oxide increased the partition coefficient by 9% for the {PEG + sodium citrate + water} system, while other nanoparticles had no effect or decreased the partition coefficient. To investigate the effect of GO concentration on the partition coefficient, various concentrations ranging from 0.005 to 0.04 wt % was examined. It is observed that at a GO concentration equal to 0.01 wt %, the maximum partition coefficient improvement is achievable to be 59%. The highest partition coefficient 5.74 was obtained for the system {PEG6000 19 wt %, sodium citrate 10 wt %, and GO 0.01 wt %}. It can be concluded that a trace amount of nanoparticles can change the partition coefficient either by increasing or decreasing. It seems that the concentration of nanoparticle also has a significant effect on the partition coefficient.