A hybrid architecture system was developed via in situ formation of SiO 2 nanoparticles in the cavities of COOH-terminated hyperbranched aromatic polyester (CHBPE). Results show that SiO 2 nanoparticles can be successfully anchored in the cavities of CHBPE owing to the hyperbranched structure of CHBPE. The resulting CHBPE-SiO 2 system is applied to epoxy (EP) resins using 4,4 0 -diaminodiphenyl sulfone (DDS) as curing agent. Because -COOH groups in CHBPE-SiO 2 system can react with epoxy groups, the conversion of epoxy groups in EP/CHBPE-SiO 2 systems can be improved, and the strong interface interaction between EP matrix and CHBPE-SiO 2 can be realized. The resulting EP/CHBPE-SiO 2 composites have excellent mechanical property. When the contents of CHBPE-SiO 2 are 8%-20%, the impact strengths, the flexural strengths and the tensile strengths of EP/CHBPE-SiO 2 composites can reach 24-46 kJ/m 2 , 121-165 MPa and 57-71 MPa, respectively, which are 16.1-31.9-fold, 4.0-5.9-fold and 8.9-11.3-fold higher than those of pure EP, respectively. EP/16%CHBPE-SiO 2 composites have the optimal comprehensive mechanical property. The initial thermal decomposition temperature at 5 wt% weight loss (T di ) and glass-transition temperature (T g ) of EP composites can increase by 70-84 C and 30-43 C, respectively, after introducing 8%-20% CHBPE-SiO 2 . Moreover, the dielectric constants of EP composites with 8%-20% CHBPE-SiO 2 decrease by 3%-11% as compared to pure EP. The high dispersion of SiO 2 in EP/CHBPE-SiO 2 composite and the strong interface interaction between EP matrix and CHBPE-SiO 2 can contribute to the outstanding comprehensive property of EP/CHBPE-SiO 2 composite.mechanical properties, microstructure, nanotechnology, thermal properties, thermosets | INTRODUCTIONEpoxy (EP) resins have desirable properties including excellent mechanical and electrical properties, easy processability and good chemical resistance, which allow them to be widely used in coatings, adhesives, structural composites, and electronic materials. [1][2][3][4][5][6] However, the poor toughness of EP matrix, resulting from the high crosslinking density, [7][8][9] severely limits its application in requiring high impact strength. [10][11][12][13][14] Therefore, much