Epoxy that used as insulating material in electronic and electrical devices plays an important role in system reliability. Addition of nanoparticles can improve the insulating properties of epoxy compared with undoped material. However, due to the change of the material structure, trap characteristics and charge behaviors are altered as a consequence. This possibly leads to the distortion of electric field that initiates discharge which results in the degradation of the insulation. From the viewpoint of safety, it is necessary to investigate the charge behavior of epoxy nanocomposites. This paper presents study aimed at clarifying the effect of nano-filler concentration on the surface charge accumulation and the decay behaviors of epoxy/Al₂O₃ nanocomposites. Samples were prepared by dispersing nano-scale Al₂O₃ into epoxy. Corona charging tests were performed at room temperature with a relative humidity of less than 40%. The charge distribution was measured by means of an electrostatic voltmeter. Obtained results show the dependence of the charge density as well as the charge decay rate upon the concentration of Al₂O₃, varying as a function of the charge polarity, charging time and charging voltage. It is suggested that the charge dynamics is dependent upon the characteristics of localized surface states that are altered by the nanoparticles.