A ternary miscible blend system comprising only crystallizable aryl polyesters [poly(ethylene tereplithalate), poly(trimethylene terephthalate), and poly(butylene terephthalate)] was characterized with the criteria of thermal analyses, microscopy, and X-ray characterizations. The reported ternary miscibility (in the quenched amorphous state of blends of the three aryl polyesters) was truly physical and under the condition of no chemical transesterifications; this justified that transesterification was not a necessary condition for miscibility in polyester blends in this case. This study further proposed and tested a novel concept of a new criterion for miscibility characterization for polymer blends of only crystallizable polymers. A single composition-dependent cold-crystallization-temperature (T-cc) peak in blends of only semicrystalline polymers was taken as an indication of an intimate mixing state of miscibility. The theoretical background for establishing the single composition-dependent T-cc peak as a valid miscibility criterion for crystallizable polymer blends was examined. (C) 2003 Wiley Periodicals, Inc.