Abstract: The application of nanoparticles (NPs) in enhanced oil recovery (EOR) offers a practical approach to resolving some surface-related problems encountered in contemporary technological processes. In this study, graphene oxide nanosheets (GONs) were synthesized by Hummer's method and, then, were subjected to surface modification by hexamethyldisilazane (HMDS) and diazonium sulfonic (DS) compounds. The new combination was known as GO-Su-HMDS. The potential stability of GO-Su-HMDS nanofluids (NFs) was investigated using the zeta (ζ) potential test. A comparative study of the effect of the synthesized NFs on wettability alteration of the reservoir rock was performed using interfacial tension (IFT) and contact angle experiments. According to the results of this study, the contact angle decreased from the initial value of 161° (oil wet) to 35° (water wet). In addition, IFT decreased from 18.45 mN/m for deionized (DI) water to 8.8 mN/m for 500 ppm GO-Su-HMDS NF. Moreover, the results of flooding experiments showed that the NPs of a GO-Su-HMDS concentration of 400 and 500 ppm could increase the oil recovery by 20% and 19%, respectively. The experimental results showed that GO-Su-HMDS NFs with a concentration of 500 ppm have the best efficiency in terms of altering the wettability of the rock from oil wet to water wet. Thus, it can be said that this nanofluid can reduce the contact angle and IFT and also increase the sweeping efficiency of oil.