Abstract: Poly(ethylene terephthalate) (PET) was modified by blending with hyperbranched polyester (HBP) with terminal groups of hydroxyl, hexadecyl and phenyl.The effects of types and dosage of terminal groups of HBP on tensile strength, impact strength, crystallization and dynamic viscoelastic properties of HBP/PET composites were studied.The results show that when the mass fraction of phenyl-terminated HBP (HBP-Bz), hexadecyl-terminated HBP (HBP-C16) and hydroxyl-terminated HBP (HBP-OH) are 0.1%, 0.4% and 0.2%, respectively, the tensile strength and impact strength of HBP/PET composites reach the maximum.HBP improves the degree of crystallinity when the mass fraction of HBP is in the range of 0.1%-0.4%.Compared with HBP-C16 and HBP-OH, HBP-Bz dramatically accelerates the crystallization rate of PET.The lower mass fraction (0.1%-0.4%) of HBP plays a tackifying role in the blended systems of PET.HBP/PET composite melt exhibits the rheological behavior of typical pseudoplastic fluids.To some extent, the addition of HBP increases the macromolecular chain entanglement and physical junction of PET, and the tensile strength, impact strength and melt viscosity of HBP/PET composites are improved.