We have grown titanium dioxide and suboxide thin films using reactive direct-current magnetron sputtering methods. By monitoring the discharge voltage and plasma optical emission spectra at a constant current mode during the growth, we identified the oxidized conditions of metal target as well as the energy of plasma species, which characteristics were directly revealed in the structural and chemical properties of as-grown titanium oxide thin films. The films with a higher discharge voltage and a higher population of TiO* plasma turned out to have a dioxide configuration while ones with a lower voltage and a higher Ti* plasma are of multiple phases with suboxide counterparts.