The effects of oxygen partial pressure and a Cu catalyst on the growth of Zn2GeO4 nanowires (NWs) on Si substrates by thermal evaporation of ZnS and Ge powders at 1000-1100 degrees C in Ar were studied. The Zn2GeO4 NWs could grow on the bare Si substrates at 650-800 degrees C in Ar, while a deposited Cu layer further enhanced their growth, forming the Cu-doped Zn2GeO4 NWs. The growth of both the Zn2GeO4 and Cu-doped Zn2GeO4 NWs followed the self-catalyzed vapor-liquid-solid process. In Ar/O-2 (3%), GeO2 nanoparticles instead of Zn2GeO4 NWs predominantly formed on the Si substrates, revealing that the higher oxygen partial pressure in Ar enhanced the growth of GeO2. The green emission peak of Cu-doped Zn2GeO4 NWs showed a blueshift of about 25 nm relative to that of the undoped Zn2GeO4 NWs.