The phase behavior of binary mixtures containing hyperbranched polyester Boltron 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 lattice-cluster 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.