Abstract: The invention relates to a method of preparing dinitramidic acid HN(NO.sub.2).sub.2 and salts thereof having the formula M.sup.+n (.sup.- N(NO.sub.2).sub.2).sub.n, wherein M is a metal cation or a nitrogen-containing cation and n=1-3. The dinitramide salt can be used as oxidiser in solid propellants. Dinitramidic acid is prepared by nitration of a compound selected from a group consisting of NH.sub.2 NO.sub.2, NH.sub.4 NH.sub.2 CO.sub.2 ; NH.sub.2 SO.sub.3 H, NH(SO.sub.3 H).sub.2, N(SO.sub.3 H).sub.3, and its salts with metal cations or organic cations, e.g. NH(SO.sub.3 NH.sub.4).sub.2, and other products formed when ammonia is reacted with sulphuric trioxide, with a common nitrating acid such as nitric acid/sulphuric acid or nitric acid/acetic anhydride. The invention also relates to a method of preparing dinitramide salt, comprising neutralisation of dinitramidic acid with a neutralising agent, e.g. ammonia, and recovery of the dinitramide salt from a mixture of salts formed in the neutralisation.