One-step gamma radiation aided method was adopted to synthesize face centre cubic structured Silver-Gold alloy nanoparticles (Ag-AuNPs)having particle size ∼10 nm and simultaneously diffused into Polycarbonate (PC). The depth of diffusion of Ag-AuNPs in PC was found to be 93 nm at a dose of 600 kGy. A broad peak around 492 nm in absorbance spectra was due to the surface plasmon resonance of Ag-AuNPs. X-ray Photoelectron spectroscopic results showed blue shift in Au 4f and Ag 3d peaks indicating the possible interaction of Ag-AuNPs with PC. The Ag-AuNPs diffused PC showed enhancement in catalytic reduction activity due to more adsorption and effective electron transfer from Ag-AuNPs to 4-Nitrophenol.