The growth process of germanium nanocrystals in a SiOx matrix was studied by an x-ray diffraction (XRD) technique using the grazing incidence of x rays. The conclusion based on the XRD analysis of the Ge-doped glass is in good agreement with that from Raman spectroscopy and x-ray photoelectron spectroscopy. There are two stages of crystallization: the first stage is nucleation of the Ge nanocrystals at 600 degrees C, and the second stage is growth of the nanocrystals at 800 degrees C. During the second stage, the decomposition of GeOx into Ge and O in the Ge-doped glass sample results in fast growth of Ge nanocrystals. This is the first report that studied the growth of Ge nanocrystals in an SiOx matrix by XRD.