Hydroxy-terminated hyperbranched polyester (HBPE) was synthesized via one-step method by using trimethylolpropane (TMP) as core and 2,2-dimethylolpropionic acid (DMPA) as monomer. Subsequently, HBPE was added to polycarbonate (PC) as a modifier. The PC/HBPE blends were characterized by Fouriertransform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), universal tensile testing machine, rotational rheometer, and melt flow indexer (MFR). The results indicate that with the addition of HBPE, the glass transition temperature of PC/HBPE blends is decreased from 147.5 ℃ to 130.7 ℃ , demonstrating that the flexibility of PC chains is enhanced by the addition of HBPE. When the content of HBPE is 2 phr, a 7.1% increase in fracture strength (to 64.6 MPa) of PC / HBPE blend compared to pure PC is observed; when the HBPE content is 5 phr, increases of 29.4% , 136.8% , and 59.3% in elongation at break, notched impact strength, and tensile toughness of PC/HBPE blend compared to pure PC are seen respectively. Melt flow index testing reveals that when the HBPE content is 5 phr, the melt flow index is increased by 288.4% compared to pure PC, suggesting that the melt viscosity of PC is reduced by the addition of HBPE. Therefore, HBPE is an excellent toughening, strengthening, and plasticizing modifier, with broad application prospects.