Graphene has become a hot research topic in fundamental physics, nanoelectronics, photonics, chemistry and materials science since 2004. Besides being a precursor for chemical production to produce graphene with large scale and low cost, graphene oxide (GO) holds unique structural, chemical, physical, electrical and optical properties, which make it another important nanomaterial for both fundamental study and industrial applications. This thesis focuses on how to improve the production method and graphitization of GO, and how to explore the large size and high crystalline quality graphene. A series of researches were performed on preparation of ultra-large GO, graphitization of GO by different routes, and evaluation of graphitized samples by Raman spectroscopy, electrical measurements of field-effect transistors (FET).