Abstract: 15 new borane anion ammonium salts have been synthesized by the reaction of borane anion (arachno-B₃H₈^- or closo-B₁₀H₁₀^2-) with various ammonium halides. All of the compounds were confirmed by elemental analysis and IR. The DTAresults for these compounds indicated that the thermal stabilities of the B₁₀H₁₀^2- salts are higher than those of B₃H₈^-, and the thermal stabilities of these compounds become lower when an alkyl group in the ammonium cation is substituted by an amino group. The greater the number of amino groups, the more the thermal stability decreases,