Nanosized indium oxide (In2O3) particles, dispersed within pores of mesoporous silica, were synthesized by soaking and thermal decomposition of indium sulfate. The particles were characterized by transmission electron microscopy (TEM) and nitrogen sorption isotherms. Photoluminescence spectra of the samples annealed at different temperatures were measured. It was shown that the In2O3 nanoparticles were isolated from each other and highly uniformly dispersed inside the pores of silica host, which were less than 8 nm in diameter. New photoluminescences were observed for the samples annealed at different temperatures.