The phase behavior of binary mixtures containing hyperbranched polyester Boltorn U-3000 and organic solvents such as hydrocarbon, ether, and linear aliphatic 1-alcohol was studied in the temperature range from about 250 K up to the boiling point of the solvent. The polymer is completely soluble in hydrocarbons (hexane, heptane, benzene, toluene) and ethers (methyl-tert-butyl ether, MTBE, or ethyl-tert-butyl ether, ETBE) but only partially miscible with alcohols. Liquid-liquid phase equilibria (LLE) diagrams have been determined for binary systems containing the polymer and methanol, ethanol, 1-propanol, or 1-butanol. The solubility of the polymer in alcohols increases with an increase of the chain length of the solvent. Corresponding LLE phase diagrams in 1-propanol and 1-butanol, including spinodal as well as binodal liquid-liquid coexistence curves, were calculated in terms of the statistical mechanics based on the latticecluster theory, based only on the upper critical solution temperature and the polymer chain architecture. The results show a semi-qualitative agreement of predicted and experimental equilibrium compositions and temperatures.