We have investigated the effect of annealing temperature on the structural property of Au thin films deposited on Si(100) substrate using the radio frequency (RF) magnetron sputtering technique. X-ray diffraction revealed that the relative intensities and FWHM of (111), (200), and (311) peaks increased and decreased, respectively, after thermal annealing at 600 C. Scanning electron microscopy indicated that after annealing at 600-700 degrees C, Au structures agglomerated on Si(100) surfaces. Energy dispersive x-ray spectrometry (EDX) revealed that the agglomerated structure was composed of pure Au.