Cephalexin is an important antibiotic. It is very significant to determine an appropriate method for the extraction of this valuable antibiotic for industrial applications. Aiming at developing an efficient method for the extraction of cephalexin, the partitioning of cephalexin has been evaluated in aqueous two-phase system, including cholinium chloride and potassium phosphate. The effect of three main and independent variables on the partition coefficient of cephalexin has been estimated. These variables are as follows: equilibrium temperature, different weight percent of salt, and cholinium chloride. The results showed that by increasing the salt weight percent and the temperature, the partition coefficient of cephalexin will increase, while by increasing the weight percent of cholinium chloride, its partition coefficient will decrease.