Separation of 1,3-propanediol from a fermentation broth is a difficult task that has become a bottleneck in industrial production. Aqueous two-phase systems composed of hydrophilic solvents and inorganic salts could be used to extract 1,3-propanediol from fermentation broth. The ethanol/ammonium sulfate system was investigated in detail, including phase diagram, effect of phase composition on partition, removal of cells and biomacromolecules from the broth. The results indicated that 1,3-propanediol took part in forming phases and had little effect on its partition. The highest partition coefficient (4.77) and recovery (93.7%) of 1,3-propanediol was obtained with an aqueous two-phase system composed of 46% (v/v) ethanol and saturated ammonium sulfate. At the same time the byproducts, 2,3-butandiol and acetoin, were also extracted with high efficiency. The maximum selective coefficient of 1,3-propanediol to glycerol was 6.0 in the experimental range. In addition, cells and proteins could be simultaneously removed from the fermentation broth, and the removal ratio for cells and proteins reached 99.7% and 79.0%, respectively. (C) 2009 Elsevier B.V. All rights reserved.