Aqueous two-phase systems (ATPSs) have been recognized as potential alternative techniques for extraction or purification of biomolecules. In this work, partitioning behavior of cefazolin has been investigated in polymer-salt ATPSs. Thus, systems containing polyethylene glycol (PEG) with two different molecular weights (6000 and 8000) and three forms of sodium salts, including sodium citrate, sodium tartrate, and sodium sulfate were examined. Firstly, the binodal curves were determined at 300 K and then correlated with Merchuk equation. Results indicate that the system PEG8000/sulfate owns a wider two-phase area. Then, the tie-lines were plotted for the systems under study, and their validity was evaluated using the Othmer-Tobias and Bancroft equations. Finally, the partition coefficient of cefazolin was investigated in 6 different two-phase systems and 28 tie-lines overall. Effect of salt type, polymer molecular weight and its concentration on partition coefficient were discussed. On the basis of the results it can be declared that as the polymer concentration increases, the partition coefficient increases but the increase of polymer molecular weight leads to partition coefficient reduction. Sodium citrate was better than the other salts used for studying the cefazolin partitioning, that is in good accordance with the excluded volume theory. The maximum amount of partition coefficient equals to 13.4 with a 90.5 recovery percentage in the top phase which belongs to the system combined of PEG6000 (16% w/w) and sodium citrate (14% w/w). (C) 2019 Elsevier B.V. All rights reserved.