The present invention relates to an improved process for processing the reaction mixture from the direct oxidation of hydrocarbon into carboxylic acid, using molecular oxygen or a gas containing it, in the liquid phase, in a solvent and in the presence of a catalyst dissolved in the reaction medium, characterized in that the said process comprises: when the composition of the reaction mixture allows it, a decantation into two liquid phases: a nonpolar upper phase and a polar lower phase; a distillation of the said lower phase or, where appropriate, of all of the reaction mixture, thus separating, on the one hand, a distillate and, on the other hand, the distillation residue comprising the acids formed, the catalyst, the heavy compounds, at least some of the solvent and, if any, the reaction intermediates and side products; a purification treatment by oxidation, using molecular oxygen or a gas containing it or using oxygen donors, of the distillation residue obtained above, a distillation of the reaction solvent and the reaction intermediates and side products which may still remain in the mixture, a crystallization of the carboxylic acid produced in the reaction; a recrystallization from water of the carboxylic acid produced in the reaction.