Nanocrystalline Ge SiO 2 thin films were successfully prepared by the ion beam sputtering technique followed by annealing. Optical absorption spectra of the Ge crystallites of size 3 to 9 nm in diameter, on the average, have been studied. In comparison with that of the bulk Ge crystals, the nanocrystalline Ge show a blue shift of energy and the optical band gap increases with decreasing of the particle size of the nanocrystallites. The effective mass approximation model based on the quantum size effect is suggested to discuss the observed optical experimental details with satisfaction but only qualitatively. An effect of the dielectric confinement of the Ge nanocrystallites on the optical absorption spectra was observed.