Melt blends of poly(trimethylene terephthalate) (PTT) and poly(ethylene terephthalate) (PET) of various ratios were prepared by mixing at $280^{circ}C$ for different times using twin screw type internal mixer, and their thermal properties were investigated by DSC, DMA and NMR spectroscopy. With increase in mixing time at $280^{circ}C$, the two melting peaks of PTT/PET blends, corresponding to the melting of PTT and PET, merged to one peak and moved to lower temperatures, while the crystallization temperature moved to higher temperatures. DMA analysis indicated a single glass transition temperature for the PTT/PET melt blends of various compositions prepared by mixing at $280^{circ}C$ for 5 minutes, indicating that the blends are completely miscible in the amorphous region. The transesterification reaction in the PTT/PET melt blends was confirmed bi NMR spectroscopic analysis. Degree of randomness and sequence length of the blends were calculated by using $^13C-NMR$ data. The former increased while the latter decreased as the melt mixing time increased.