The partitioning of Canavalia brasiliensis (ConBr) lectin from Canavalia brasiliensis seeds was carried out in aqueous two-phase systems composed of polyethylene glycol (PEG) and sodium citrate. The effect of PEG molecular weight (600, 1000, 2000, and 3350), pH (6.0, 7.0, and 8.0) and ionic strength (0, 2, 5, and 10% NaCl) on the partition behavior of ConBr in ATPS was systematically investigated. Liquid-liquid equilibrium data for the PEG 600-sodium citrate system at pH 6.0, 7.0, and 8.0 were determined at 25 degrees C. The effect of the pH on the position of the binodal curves was not significant, but it had a strong influence in the partitioning of the ConBr. An increase in the NaCl concentration significantly favored the partitioning of ConBr to the top phase, probably due the dehydration of the protein molecules triggered by high ionic strength. The best system for purification of ConBr was composed by 17.54% PEG 600, 15.14% sodium citrate, 5% NaCl at pH 8.0 with recovery yield 70% and 98% purity. This system was found suitable for the recovery of ConBr, since it not only allowed the partitioning of the lectin towards the PEG-rich phase but also the concentration of contaminants in the salt-rich phase.