Gold nanoparticles (AuNPs) offer a great promising in biomedical applications.Since nanoparticle size has been shown to be an important parameter affecting the nanoparticle uptake and cellular internalization. We investigated the effects of gamma radiation and nanoparticle size on the dielectric properties of AuNPs. The dielectric data of AuNPs indicates that it has a strong dielectric dispersion in the frequency range of 20 Hz-100 kHz which was particles size dependent. There are relatively significant increase of both the electrical permittivity (ε¢) and conductivity (s) according to the irradiation dose. Moreover, ε¢ and s had higher values as size of the AuNPs increases. AuNPs of 5 nm size are preferable to use them in tumor therapy. The presented work aims to characterize and improve the quality control of AuNPs, define the benefit combination effects of size and gamma irradiation on the properties of AuNPs dielectric relaxation spectroscopy.