Abstract: A method of making finely particulate ammonium perchlorate which comprises establishing a two-phase liquid system in which the upper phase is a concentrated solution of ammonium perchlorate and the lower phase is a liquid which is immiscible with the upper phase solvent and a non-solvent for ammonium perchlorate. Precipitation of ammonium perchlorate from the solution into the non-solvent is effected by either cooling the solution or evaporating the solvent thereof while subjecting the system to ultra-sonic vibrations. Fine ammonium perchlorate particles collect in the non-solvent phase and are recovered therefrom.