We establish a new melting-point-depression theory, based on the modified-double-lattice model, that takes into account the local composition concept to describe the phase behaviors of solid-polymer-electrolyte/ salt systems (modified-double-lattice/nonrandom model). In comparison with experimental data, quantitative descriptions of the proposed model show better agreement for the given systems than those of the modified-double-lattice model. The systems studied in this work are combinations of poly(ethylene oxide) and zinc halides and of poly(ethylene oxide) and LiCF3SO3. The results show that the nonrandomness effect of the salt distribution plays a major role in determining the eutectic points of the given systems. (C) 2004 Wiley Periodicals, Inc.