The research proposes a novel water-soluble silk fibroin nanoparticles (WSSF-NPs) created by electron beam irradiation. In this report, we demonstrate the effects of electron beam irradiation doses ranging from 1 to 30kGy on the molecular weight (MW), nanostructure formation, antioxidant activity and reducing power of the WSSF-NPs. Electron beam-induced degradation of SF causing MW reduction from 250 to 37kDa. Chemical characteristic functions of SF still remained after exposing to electron beam. The WSSF-NPs with the MW of 37kDa exhibited spherical morphology with a nanoscaled size of 40nm. Antioxidant activities and reducing powers were investigated using 2,2-diphenyl-1-picrylhryl free radical (DPPH∙) scavenging activity and ferric reducing antioxidant power (FRAP) assays, respectively. The WSSF-NPs showed greater antioxidant activity and reducing power than non-irradiated SF. By increasing their antioxidant and reducing power efficiencies, WSSF-NPs potentially created gold nanocolloid. WSSF-NPs produced by electron beam irradiation would be a great merit for the uses as a natural antioxidant additive and a green reducing agent in biomedical, cosmetic and food applications.