The facile one-step synthesis of AlOOH–Ag nanocomposite has been performed. Bimetallic Al–Ag nanoparticles prepared by electrical explosion of Al and Ag wires were used as a precursor. AlAg nanoparticles consisted of a supersaturated Al–6 at% Ag solid solution and Ag-rich Guinier–Preston zone several nanometer in diameter that were not detected by XRD due to their extremely small size and peculiarities of their crystal structure. An environmentally friendly process of water oxidation at 60 C was used to convert Al–Ag nanoparticles into AlOOH–Ag nanocomposites. In the course of oxidation, chemical dealloying of Al–Ag solid solution took place yielding porous agglomerates with inclusions of very fine 5–30 nm Ag nanoparticles. The agglomerates consisted of 2–5 nm thick crumpled nanosheets of boehmite 200 nm in size. The synthesized AlOOH–Ag nanocomposites possessed high antibacterial activity against both Gram-negative and Gram-positive microorganisms as indicated by the time-kill assay. The presented results open up new processing possibilities of metal-oxide composite nanostructures with attractive properties that can be used in catalysis, water purification and biomedical applications.