The n-decane fuel/n-decane-based nanofluid fuel could be one of the most promising alternative fuels as aviation kerosene for aerospace application. This paper proposes Al/n-decane nanofluid fuel with the surfactant of sorbitan monooleate (SP-80) and investigates the size effect of Al nanoparticle (SA, 56.0 nm; SB, 74.4 nm,; SC, 93.4 nm) on its dispersion stability, physical properties, and electrostatic breakup performance. Dynamic light scattering (DLS) measurements and numerical calculations of particle collision demonstrate that the nanofluid fuel containing SC has the lowest agglomeration and the best stability. The addition of Al nanoparticles slightly influences the physical properties of surfactant-loaded n-decane. At the same Al nanoparticle concentration, the surface tension of the nanofluid fuels reduces at elevated Al nanoparticle size, while the viscosity increases. In a strong electric field, Al nanoparticle size presents a nonmonotonic effect on the average breakup droplet diameter. The force analysis and characteristic dimensionless parameter evaluation demonstrate that it has a synergetic effect with the electrification on electrostatic breakup of the nanofluid fuels. The nanofluid fuel containing SC achieves the smallest average breakup droplet diameter of 56.7 mu m, which is much finer than that of surfactant-loaded base fluid. Therefore, the electrostatic breakup performance of the nanofluid fuels depends on the comprehensive effect of nanoparticle size on dispersion stability, physical properties, and electrification.