Hyperbranched polymers have increased attention because of their branched structure and the wide range of different functional groups. Because of this feature hyperbranched polymers show an excellent applicability for aqueous two-phase systems (ATPS). In this work an ATPS consisting of a PEG-functionalized hyperbranched polyesteramide + water + Dextran T40 is compared to an ATPS consisting of PEG8000 + Dextran 140 + water. In addition to the experimental investigation of the ATPS, they will also be modeled using the lattice cluster theory (LCT) in combination with Wertheim theory. The LCT allows the direct incorporation of the polymer architecture in the Helmholtz free energy, so all derived properties are dependent on chain architecture. A multicomponent version of LCT for incompressible polymer solutions/blends is presented in this work. To consider associative interactions the LCT is combined with Wertheim association theory. To obtain the model binary interaction parameters of the hyperbranched polymer + water the subsystem hyperbranched polymer + water was experimentally estimated, and for the subsystem PEG8000-water experimental data from literature were used, the parameters were fitted in both cases. So both ATPS could be modeled. In addition to the phase behavior, the kinematic viscosity of both ATPS was compared. (C) 2013 Elsevier B.V. All rights reserved.