A method for producing a preparation containing a bioactive substance, characterized in that it comprises forming a solid material containing the bioactive substance and a polymer, and contacting the solid material with a high pressure gas. The method allows the production of a preparation which is suppressed in excessive initial release of the bioactive substance immediately after the administration thereof, is capable of releasing a predetermined amount of the bioactive substance over a long period of time, and is extremely reduced in the deterioration of the bioactive substance and in the amount of a residual organic solvent.