A subject-matter of the present invention is a novel process for the synthesis of hexanitrohexaazaisowurtzitane (HNIW), a compound of use as energetic filler in powders, propellants and explosives.This process comprises a first stage of reaction of an .alpha.,.beta.-dicarbonyl derivative with a primary amine which makes it possible to form a hexasubstituted hexaazaisowurtzitane derivative.The HNIW is subsequently obtained directly, in a single reaction stage, by nitration of the hexasubstituted hexaazaisowurtzitane derivative.This process, in only 2 stages starting from a primary amine, is particularly simple and inexpensive.