Spherical gold nanoparticles with diameters less than 8 nm have been prepared by the photoinduced reduction of hydrogen tetrachloroaurate via a one-step sol-gel process. The as-prepared Au nanoparticles are highly dispersed in a mesoporous TiO2 gel monolith and are exposed to the external ambient atmosphere with a surface plasmon resonance absorption band centered at 578 nm. The results show that the size, size distribution, and dispersion of Au nanoparticles in the titania monolith are strongly dependent on the ultraviolet irradiation time of AuCl(4)(-) ions in the titania sol. The Au nanoparticles are found to be more uniform and smaller in size and more highly dispersed in the titania monolith with longer irradiation time. The crystallization of titania from the amorphous phase to the anatase phase is found to be suppressed at room temperature, and this is attributed to the smaller and highly dispersed Au nanoparticles on the surface of the colloids of titania.