Abstract: The polymethyl methacrylate(PMMA)@polybutadiene(PB) core-shell structured nanoparticles toughened bisphenol A-cyanate(BADCy) resin was prepared. The mechanical property results show that the PMMA@PB/BADCy resin presents excellent toughness when 6wt% of PMMA@PB core-shell rubber is used. And the impact strength of the PMMA@PB/BADCy resin with 6wt% of PMMA@PB core-shell rubber is 14.32 kJ·m^-2, increased by 83.6%. The thermal performances of toughened resin were investigated by DMA and TG-DTA as well. The results show that when 6wt% of PMMA@PB core-shell rubber is used, the glass transition temperature of the cured PMMA@PB/BADCy resin is 236.8℃ and the temperature of maximum degradation rate is 410.0℃. TEM images show that the PMMA@PB core-shell rubber has good dispersion in BADCy resin. SEM images show that the fracture surface of PMMA@PB core-shell rubber toughened BADCy resin exhibits typical toughness fracture. The rheological properties of the PMMA@PB/BADCy resin show that the PMMA@PB core-shell rubber has insignificant influence on the rheological properties of BADCy resin. The lowest viscosity of the PMMA@PB/BADCy resin is 0.79 Pa·s, which is the ideal viscosity to impregnate fiber for preparing prepreg. The dielectric properties at different frequencies show that the PMMA@PB core-shell rubber has little effect on the dielectric properties of toughened BADCy. When 6wt% PMMA@PB core-shell rubber is used, the dielectric constant is 3.0 and the dielectric loss is about 0.010. The PMMA@PB/BADCy resin system presents excellent performances and can be used as matrix of prepreg. It is suitable for the manufacture of low dielectric composites in aerospace.