The relationship between the defects of reduced graphene oxide (RGO) and the oxidation degree of graphite in the preparation of graphene with chemical conversion method has been studied in this work This study was performed on an artificial graphite through the measurements of X ray diffraction, Raman spectroscopy and particle size analysis. The experimental results have shown that there indeed was a close relationship between the defects and the oxidation degree, which appeared in the form of S-type curve. Also, it was found that a low KMnO4 addition would lead to a partial oxidation of graphite, leaving defects mainly on the edges of RGO; with a high KMnO4 addition, the defects on RGO mostly appeared on the surfaces. (C) 2015 Elsevier Inc. All rights reserved.