We have derived a new molecular thermodynamic model based on the lattice cluster model and melting point depression theory to account for the structural effect on phase behaviors of hyperbranched solid polymer electrolyte/salt systems. The two structural parameters (the generation number and separator length) are introduced to characterize the architecture of the hyperbranched polymer. A thermooptical analysis technique is used to determine the melting points of hyperbranched polymer/ZnI2 systems. Our results show that the eutectic point is presented at a higher weight fraction of the salt as the generation number increases. (C) 2004 Wiley Periodicals, Inc.