Graphene with ultra-lightweight property and atomic monolayer structure is one of the most interesting new materials in the world nowadays. In this paper, the authors report the synthesis of graphene oxide (GO) by a modified Hummer method. The structure and morphology of GO were investigated by several methods such as X-ray diffiaction (XRD), Fourier transform infrared spectroscopy (FTIR), field-emission transmission electron microscopy (FETEM) and field emission scanning electron microscopy (FESEM). The results show that the GO samples are single phase and micrometer-sized sheets. FTIR measurements confirmed the existence of oxygen-containing functional groups on the surface of the GO sheets. With stable and highly reproducible synthesis process and the ability to produce in large quantity, the GO sheets obtained in the research can be used as new and potential materials for applications in biology, biological chemistry and fluorescent biosensors.