In national defense, aluminum nanoparticles (Al NPs) have better combustion performance than Al microparticles but are easily oxidized during processing, especially in oxidative liquids. Although some protective coatings have been reported, it is still challenging to obtain Al NPs stable in oxidative liquids (e.g., hot liquids) without scarifying combustion performance. Here, we report ultrastable Al NPs with enhanced combustion performance enabled by the crosslinked polydopamine/polyethyleneimine (PDA/PEI) nanocoating merely ∼15 nm in thickness and ∼0.24 wt % in mass. The Al@PDA/PEI NPs are fabricated by one-step rapid graft copolymerization of dopamine and PEI on Al NPs at room temperature. The formation mechanism of the nanocoating is discussed including reactions between dopamine and PEI and interactions of the nanocoating with Al NPs. The Al@PDA/PEI NPs show excellent stability in hot water, and the mechanism is interpreted by molecular dynamics simulation. The PDA/PEI nanocoating can also enhance the combustion heat and burning rate of Al NPs