Poly (ethylene terephthalate)/poly (trimethylene terephthalate) (PET/PTT) blends were prepared and their melting and crystallization properties were investigated by differential scanning calorimetry (DSC). The glass transition temperatures suggest apparently that PET and PTT have good miscibility at amorphous state. The blends with more PET content less likely undergo a melting/recrystallization process during DSC heating scan. In the blends, PET component with higher supercooling degree will crystallize first, and then the crystallites of PET will be the nucleating agents for PTT, which greatly improves the crystallization rate of PTT.