A method for preparing an acetazolamide microparticle having a mean particle size ranged between 0.36 μm and 18 μm is provided. The method includes steps of dissolving an acetazolamide in a solvent to form an acetazolamide solution； and mixing the acetazolamide solution with a supercritical fluid at a temperature and a pressure above a critical point of the supercritical fluid for forming the acetazolamide microparticle, wherein the solvent is miscible with the supercritical fluid.
