Graphene reveals different doping behaviors depending on supporting substrates. It exhibits p- or n-type doping behaviors via charge transfer with the substrates. In this study, we have investigated the doping effect in graphene on oxide substrates such as MgO and SiO2 using first-principles calculations. For investigation of different doping behaviors in graphene on oxides, we consider ideal oxygen(0)terminated and fully hydroxylated surface for each substrate. Our results indicate that graphene reveals a p-type behavior on O-terminated MgO(111) with oxidized carbon layer, while showing an n-type behavior on hydroxylated MgO(111). In the case of graphene adsorbed on SiO2(0001), very small (or negligible) doping occurs in graphene. Details in doping behaviors in graphene are analyzed in terms of charge density difference, partial density of states and energy band structure. (C) 2015 Elsevier B.V. All rights reserved.