Abstract: Polybutylene terephthalate (PBT) is a semi-crystalline thermoplastic polymer with excellent dimensional stability, high stiffness and hardness, good chemical resistance, mechanical properties and processability. But its impact resistance is low and toughness is poor. PBT was melt blended with poly(butylene succinate-co-butylene diphenyl ether dicarboxylate) (PBSO), which has excellent toughness, to improve the toughness of PBT. Firstly, PBSO was synthesized by a two-step method of esterification and polycondensation, using diphenyl ether dicarboxylic acid (OBBA), succinic acid (SA) and butanediol (BDO) as monomers, and tetrabutyl titanate as catalyst. Then, PBSO/PBT with different mass ratios of PBSO and PBT were blended by melt-extrusion to study the toughening effect of PBSO on PBT. The mechanical toughness of blends, the compatibility of PBSO and PBT, crystallization behavior, thermal stability and rheological properties were studied. The structure of PBSO was characterized by FT-IR, ¹H NMR and GPC. The mechanical performance test show that the tensile strength of the 20wt%PBSO/PBT composite material is 40.3 MPa, the elongation at break reach to 82.1%, the breaking energy increas to 24.70 MPa, and the impact strength is 23.2 kJ/m², indicating a higher tensile strength and good toughness. Dynamic mechanical analysis (DMA) and SEM results indicate that PBSO has a compatibilizing effect on PBT, and PBSO/PBT is a partially compatible blend system. DSC and wide-angle X-ray diffraction (WAXD) results show that the addition of amorphous polymer PBSO reduce the crystallinity of PBT, but do not change the crystal structure of PBT. Thermogravimetric analysis (TGA) analysis demonstrated that the PBSO/PBT composite has a good processing thermal stability.