The work has established the change in the activity parameters of aluminum nanopowders produced by electric explosion of a wire during their storage in an airtight container. The change in the characteristics of the nanopowders using four activity parameters was measured by benchmarking their activity after the production, passivation and keeping for 10-20 days and after their storage for 16years. It was also established that after long-term storage, the temperature of oxidation initiation for the nanopowders in air has increased; the increment of mass during oxidation at up to 800 degrees C for all specimens has increased, while the content of metallic aluminum has decreased. The electrical double layer on the surface of aluminum nanoparticles during storing even in an airtight container changes with time and does not provide the protective function. In this connection, the future application of aluminum nanopowders in high-energy materials is not feasible without solving the problem of their stability. According to the results, electric-explosion aluminum nanopowder is an unstable aluminum-air system even in an airtight container.