GaAs/SiO₂nanocrystals embedded thin films have been prepared on silicon (111) wafers and optical silica plates by radio-frequency magnetron cosputtering technique and post-annealing at 673 K in vacuum. Raman spectroscopy strongly suggest the existence of GaAs nanocrystals being 3 nm in average size dispersed in SiO2 thin films. Compared with that of the bulk GaAs crystals, the optical absorption edge of GaAs nanocrystals exhibits a blue shift as large as 1.78 eV, and a few absorption peaks, which are mainly caused by the quantum confinement effect.