For the first time it has been demonstrated that polycrystalline Co films (10-300 nm) of hcp single phase can be produced on SiO2 glass substrates by a gas-flow-sputtering technique. The hcp Co films are obtained at substrate temperatures below 620 K and fcc Co films are obtained above 720 K. A mixture of hcp and fcc phases is formed between these temperatures. Gas-flow-sputtering allows the sputter deposition at high pressure in the range of 1 Torr, where sputtered particles are thermalized to the temperature of the sputtering gas; the deposition of such low kinetic energy vapor can be attributable to the formation of hcp phase for Co films.