Influence of an additive of chromium-containing Al₂O₃ nanopowders on phase transitions in aluminum oxide micropowder (a waste from alumina production) is investigated. Aluminum oxide nanopowders were synthesized by shock-wave method. Chromium compounds were introduced during the synthesis as well as following annealing of powders. Main difference between obtained chromium-containing Al₂O₃ nanopowders was their phase composition. Mixtures of nanopowders and alumina macropowders were pressed and sintered. The additive of the Al₂O₃ nanopowder that was dopped with chromium ions during the synthesis and is characterized by the prevalence of theta-phase is demonstrated to be the most perspective for ceramics fabrication on the alumina base.