Abstract: A novel nanofluid of modified carbon black (MCB) nanoparticles was initially developed for enhanced oil recovery (EOR) in low permeability reservoirs. The MCB nanoparticles were obtained via a three-step reaction involving modification by oxidation, acyl chlorination, and activated grafting. MCB nanoparticles were spherically dispersed, with an average size of 72.3 nm. Compared with carbon black (CB) nanoparticles, dispersed MCB nanoparticles can effectively reduce the oil–water interfacial tension (IFT) to 10−2 mN/m and change the surface wettability of sand particles. Based on the results of core flooding experiments, the MCB nanoparticles exhibited a better EOR capacity than surfactants and CB nanoparticles, and the final oil recovery was significantly increased by 27.27%. The core scanning test showed that the MCB nanoparticles could plug high permeability channels by adsorbing onto the surfaces of sand particles and forming larger aggregates that bridge across pores or throats, resulting in a higher swept volume. The synergistic effects of improved swept volume and oil displacement efficiency were the EOR mechanisms of the MCB nanoparticles. The studies indicate that these MCB nanoparticles have excellent potential for EOR in low permeability reservoirs.