A process for preparing amorphous paroxetine hydrochloride or sertraline hydrochloride is provided, which comprises preparing a solution in which paroxetine hydrochloride or sertraline hydrochloride and a water-soluble polymer are dissolved in a co-solvent of a volatile organic solvent and water. Said solution is dried to obtain a composition comprising amorphous paroxetine hydrochloride or sertraline hydrochloride and the water-soluble matrix.