Solution blends of poly(trimethylene terephthalate) (PTT) and poly(ethylene terephthalate) (PET) of various ratios were prepared and their miscibility and thermal properties were investigated. A single glass transition temperature (Tg), intermediate between those of two pure components, was observed at each composition in the PTT/PET blend system. This indicated that the blends of PTT/PET are completely miscible in the amorphous region. On the other hand, appearance of two melting points in the solution blends suggested that PTT and PET crystallize separately. With increase in heat treatment time in the melt state at 28$0^{circ}C$ the two melting points became a single melting point, which decreased continuously due to the formation of copolymers. Especially, the melting point of the polymer of small content in the blends disappeared more rapidly by the transesterification reaction than that of the polymer of large content. The 50/50 PTT/PET blends converted into noncrystallizable random copolymers easily. The results also showed that in the PET-rich blends the crystallization of PTT was difficult, but in the PTT-rich blends the PET easily crystallized.