Graphene oxide (GO) is known has some unique properties for various applications. GO is the oxidation form of graphene. It is synthesized from graphite through chemical oxidation. The structure of GO is different with graphite and graphene where the plane of the GO is attached with oxygen functional groups. In this research, GO was prepared by using improved Hummers' method from natural graphite powder. In addition, the effects of different reaction time of 24 hours, 48 hours, 72 hours and 96 hours on the yields of GO were studied. Results indicated that different samples of GO possessed different morphologies, attachment of functionalized groups, crystallinity and absorption peaks in Ultraviolet Visible (UV-Vis) spectroscopy. GO was characterized by using a Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD) and UV-Vis. SEM result showed platelet-like surface that appeared on the surface of GO (48 hours) as compared with GO (72 hours) where wavy wrinkled and layered-flakes, and crumpled structures were seen on GO (96 hours) surface respectively. In FTIR results, the existence of higher amount of abundant oxygen-containing functional groups was confirmed in GO (96 hours) as compared with GO (24 hours) due to the longer oxidation time. Furthermore, the absorption peak of GO was noticed at around 230?nm and the intensity of peak was increased with reaction time. By comparing these results, the oxidation of graphite to form GO can be determined accurately. Therefore, this study is a great beneficial to provide more understanding for many researchers about how to control the quality and amount of GO by varying reaction times for various applications. © 2018 Author(s).