Ultrafine (nano-sized) aluminum is a promising component for solid propellants, gel propellants, explosives, etc. The work is focused upon a problem of determining active (metallic) aluminum content in nanoAl powders as one of the characteristics of their reactivity. It is shown that the high reactivity, the presence of either the gases adsorbed or coating matter on the particle surface restricts the traditionally used permanganatometric and volumetric analytic methods. A new technique determining the active aluminum content is presented. This is the adaptation of known cerimetric method based on the analytical reaction Ce4+ + e(-) = Ce3+. The method can be applied for analysis of metallic aluminum in the probes of nanoAl (including ones with organic coating), as well as micron sized aluminum, and their condensed combustion products.