Germanium nanoparticles of different sizes in silica glasses were prepared via a sol-gel method, using Cl-3-Ge-C2H4-COOH and Si(OC2H5)(4) as the starting materials. The size of the germanium nanoparticles decreases as the heat-treatment time in a H, gas atmosphere increases, and, thus, the optical absorption edge shifts to higher energies. Silica gel glasses doped with germanium nanoparticles showed a strong room-temperature photoluminescence, with peaks at 570, 605, 676, and 730 run. The peak position of the photoluminescence spectrum scarcely depends on the heat-treatment time. However, the photoluminescence intensity increases sharply as the heat-treatment time is reduced. The photoluminescence arises from germanium clusters <1-2 nm in diameter with a molecular character, instead of from nanocrystalline germanium with the diamond structure.