We report the controlled synthesis of nanocrystalline thin films of Cu2O as well as metallic Cu on glass substrates at room temperature by the versatile high pressure magnetron sputtering technique. Deposition of nanophase materials takes place in a relatively high pressure of inert gas (2– 600 mTorr) at 300 K. The average primary grain size of the materials thus synthesized was found to lie in the 4 –14 nm range and could be controlled by proper choice of process parameters (nature and the pressure of the sputtering gas, applied power, substrate temperature, and system geometry). In general, nanocrystalline thin films were formed at 300K, while loosely aggregated nanoparticles deposited at 77K. We define the conditions under which it is possible to deposit optically transparent, nanocrystalline thin films of semiconducting, single phase Cu2O on glass or quartz. ©1999 Acta Metallurgica Inc.