The effect of O-2 partial pressure on the mechanical properties of SiO2 films deposited by rf magnetron sputtering, is studied. The sputtering rate of SiO2 in argon gas with added O-2 gas is lower than that in pure argon gas, whereas the rate is independent of O-2 partial pressure. The internal stresses in films are compressive, and the magnitude decreases from 0.8 GPa for films sputtered in pure argon gas to 0.4 GPa for films sputtered in argon gas with O-2 gas partial pressure above 9 X 10(-3) Pa. Although the internal stress decreases with increasing O-2 partial pressure, the magnitudes of hardness and adhesion increase conversely. X-ray diffraction measurements indicate that the crystal structure of sputtered SiO2 films is amorphous at all O-2 partial pressures investigated. The argon content in the film obtained from an electron probe microanalyzer decreases with increasing O-2 partial pressure. An atomic force microscopy observation reveals that the surface topography of sputtered SiO2 films show a turnover from needle structure to a spherical structure, and the fracture section varies from columnar to no discernible features as O-2 partial pressure is increased.