While SrTiO3 exhibits promising electronic transport properties, its high thermal conductivity () is detrimental for its use as a thermoelectric material. Here, we investigate the influence of oxygen non-stoichiometry on in bulk SrTiO3 ceramics. A significant reduction in was achieved in oxygen deficient SrTiO3-, owing to the presence of oxygen vacancies that act as phonon scattering centers. Upon oxidation of SrTiO3-, the of pristine SrTiO3 was recovered, suggesting that oxygen vacancies were indeed responsible for the reduction in . Raman spectroscopy was used as an independent tool to confirm the reduction of oxygen vacancies in SrTiO3- upon oxidation.