Li4Ti5O12 is considered as a promising anode material for lithium ion batteries. And its commercialization is limited by its low electronic conductivity and gas generation problem during charge and discharge process. Carbon coating is considered a good strategy to improve both the limitations simultaneously. However, whether oxygen vacancies exist in the prepared Li4Ti5O12 with organic carbon added is rarely mentioned. In this paper, Li4Ti5O12/C is prepared with citric acid as carbon source. Combined with thermogravimetric analysis, gas chromatography, structure and surface analysis, it is confirmed that reducing gases are generated from the organic carbon source to reduce part of Ti4+ to Ti3+, and oxygen vacancies appear to keep the balance. Furthermore, the decomposed gases take part of Li2O away and make some TiO2 left as an impurity to deteriorate the electrochemical performances. What's more, the material properties before and after removal of partial oxygen defects are also studied. (C) 2019 The Electrochemical Society.