The extraction of HNO, by N,N-dialkylbutanamides is investigated by distribution measurements and IR spectroscopy. A mechanism involving the competing formation of three adducts is proposed : (HNO3,)(Amide)2(HNO3,)(Amide) and (HNO3,)2,(Amide), for which the equilibrium constants for 1M amide are respectively : 0.054, 0.086, 1.35.10-5for DOi.BA and 0.043, 0.135, 5.7.10-5for DOBA. The IR spectra show, in every species, hydrogen bonds linking amide and acid. From these results and previous works on inorganic acids extraction by other ligands such as diamides and TBP, we suggest an interpretation of the acids extraction, according to the relative basicities of water, acid anion and neutral organic extractant.