This article presents the suitable chemical method for preparation of graphene oxide nanosheets. In order to examine the effects of HNO3/H2SO4 ratio on interlayer spacing and its comparison, the oxidation of graphite with HNO3 and H2SO4 in 1:2 and 1:3 volume ratios was done. Based on the reaction time and interlayer spacing, it was found that the optimum results were obtained when reaction was carried out with HNO3/H2SO4 in 1:3 volume ratio (using modified Staudenmaier method) for 4 days. Results showed that the modified Staudenmaier method improved efficiency exfoliation in oxidation process. Also, the chemical reduction of graphene oxide, which obtained using the modified Staudenmaier method, with hydroquinone and hydrazine hydrate was studied. The results indicate that use of hydrazine hydrate as the reducing agent was more beneficial than the hydroquinone. In continue, we describe the preparation of surface functionalized graphene nanosheets with octadecylamine. The products were characterized by Fourier transform infrared (FT-IR), Raman spectroscopy, X-ray diffraction (XRD), Atomic force microscopy (AFM), Field emission-scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS).