A new method for preparing multi-layered graphene oxide powder was developed. In this method, the raw material was commercially available micro-sized graphite powder. The graphite powder was milled using a high speed attritor mill to reduce the particle size of the graphite to nanometer and to exfoliate the graphite into multi-layered graphene particles. The graphene particles were then oxidized into graphene oxide (GO) using the combination of strong oxidizing agents, thermal oxidizing, and sonication. Thorough morphological characterizations have been carried out to reveal the structure and the size of GO particles. The results confirmed that the oxidation process was successful.