In this study, acrylonitrilebutadiene styrene copolymer (ABS, 5 wt%) has been dissolved at 180 oC in an epoxy resin based on diglycidyl ether of bisphenol-A, DGEBA, different ratio(3, 5, 7, 10 wt %) of MgO nanoparticles were added to mixture, it has been irradiated with Gamma radiation at (20 and 50 kGy), then the epoxy component has been crosslinked with diamine hardeners. Themicro-hardness, thermal analysis (TGA and DSC) and XRD of epoxy/ ABS nanocomposites had been investigated. The results indicated that, the micro-hardness, thermal stability and glass transition temperature (Tg) of unirradiatedna no composite increased with increasing MgO load. Also, at the same MgO percentage, the irradiated specimens at 20 kGy were gave best result to micro-hardness properties. Finally, The X-ray diffraction patterns obtained for the systems confirmed the nanodispersion of MgO in the epoxy/ABS networks. It can be seen that, the addition of magnesium oxide particles to the polymer composites and the exposure to gamma radiation is working to increase the crystallization of epoxy/ABS blend.