Abstract Distribution of nitric acid between water or aqueous of ammonium nitrate and xylene solutions of tri- n-octylmethylammonium nitrate or Nivol/2-ethylhexanol solutions of Aliquat 336 nitrate has been studied. The extraction of nitric acid has been found to increase with increasing concentration of ammonium nitrate in the aqueous phase. A mathematical model of equilibrium which includes the non-ideality in both aqueous and organic phases as well as the influence of organic diluents has been formulated and its parameters evaluated. Two complexes, QABN.HNO 3 and QABN.2HNO 3, have been assumed to exist in the organic phase. Formation of the former has been found to be more easy in xylene than in Nivol/2-ethylhexanol, while formation of the latter has been found not to depend on the diluent.