Dilute aqueous solutions with Au3+ ions and Polyethylene Glycol Monostearate are irradiated with ∼1 MeV γ-ray from 60Co source, 10 MeV pulsed electrons or 1.6 GeV carbon ions. After the irradiation, the color of solutions changes from buff yellow to reddish color. The UV-vis absorption spectra show that after the irradiation, light absorption around 530 nm appears, which corresponds to the excitation of the surface plasmon due to Au nano-particles. The result confirms that the irradiation reduces Au3+ ions in the aqueous solutions and synthesizes Au nano-particles. Size and shape of the nano-particles are examined by using 200kV transmission electron microscope. Effects of irradiation parameters (total dose and dose rate) on Au nano-particle synthesis are discussed.