Ultrafine metal particles (copper, silver, and gold) have been prepared by UV irradiation of their salts dissolved in ethanol. The photoreduction of their metal salts is greatly accelerated by using benzoin as a photoinitiator. Highly dispersed copper and silver particles are obtained through the photoreduction. In the case of gold, the average diameter of the gold particles increases from 7 to 17 nm with increasing benzoin concentration. This method has been applied to obtain silver/copper and silver/gold composite particles. The optical spectra and HRTEM show that the silver/copper composite particles are phase-separated composites of silver and copper, whose observed spectra are very similar to the theoretical spectra of silver/copper alloy particles. In the silver/gold system, the observed spectra are in good agreement with the theoretical spectra of the alloy particles since that the surface plasmon band remains as a single peak and shifts continuously by varying the silver/gold composition. This strongly suggests the formation of silver/gold alloy particles.