Graphene shells were directly formed on Al2O3 nano-particles (NPs) without the use of catalytic materials using simple thermal treatment in a C2H2 and H-2 environment. The stacking number of graphene layers increased from 3 to 7 depending on the treatment temperature. The sheet resistance of films formed using Al2O3-graphene core-shell (CS) paste was 1665 Omega/square at 1000 degrees C and 60 Omega/square at 1100 degrees C. The proposed chemical reactions on Al2O3 NPs could be summarized as formation of liquid Al due to H-2 reduction, thermal decomposition of the AlO(OH) phase, graphene shell formation due to super saturation of C-elements in the liquid Al layer, and formation of an Al4C3 phase. Moreover, the existence of trapped H2O played an important role in additional reactions and led to decomposition of the Al4C3 phase, resulting in the appearance of the alpha-Al2O3 phase. The method developed in this study is a simple one-step technique that allows Al2O3-graphene CSs to be easily fabricated within a short time. Thus, this method is expected to be applied to the formation of various metal oxide-graphene CSs. (C) 2017 Elsevier B.V. All rights reserved.