Abstract Equilibrium data were obtained for polypropylene glycol, PPG (400 and 3500)/maltodextrin, MD (1000 and 2000) aqueous two-phase systems at 25°C. Four tie lines were measured for each system. The MD concentration in top phase is very small, and in some cases MD is almost excluded from this phase. The non random two-liquid (NRTL) model was used to correlate the equilibrium data. The partitioning behaviour of bovine serum albumin (BSA), α-lactoalbumin (α-La) and β-lactoglobulin (β-Lg) was studied in PPG 400/MD systems at 25°C. For most cases the proteins partition preferentially to the top phase.