Molybdenum　oxide　films　were　deposited　on　crystalline　silicon　and　quartz　substrates　by　radio-frequency　magnetron　sputtering　of　a　Mo　target　in　oxygen　and　argon　atmosphere　at　different　oxygen　partial　pressures　in　the　range　of　0.1　similar　to　0.75　Pa　and　at　a　fixed　temperature　of　400　degrees　C　for　later　annealing.　The　influence　of　oxygen　partial　pressure　on　structural　and　chemical　composition　and　optical　property　of　the　molybdenum　oxide　semiconductor　films　were　studied　by　X-ray　diffraction　(XRD),　Fourier-infrared　spectrum　(FT-IR),　Scanning　Electron　Microscopy　(SEM)　and　Ultraviolet-Visible　spectroscopy　(UV-Vis).　X-ray　diffraction　studies　reveal　the　films　are　crystalline　in　nature　with　the　presence　of　(0k0)　reflections.　The　films　deposited　at　oxygen　partial　pressure　of　0.1　Pa　become　nearly　stoichiometric.　It　is　also　confirmed　by　the　Fourier　transform　infrared　spectroscopic　studies.　Smooth　surface　topography　and　uniformly　distributed　particles　of　films　on　observed　by　SEM.　The　average　optical　transmittance　of　the　films　increases　from　74%　to　86%　with　increasing　oxygen　partial　pressure　from　0.1　Pa　to　0.75　Pa　between　360　nm　and　1400　nm,　and　the　optical　band　gap　of　the　films　increases　from　2.995　to　3.123eV　with　the　increase　of　oxygen　partial　pressure　from　0.1　to　0.75　Pa.