The present invention relates to a process for producing a pharmaceutical composition which can stably contain an active ingredient unstable against water and can sustained-release such the active ingredient for a long period of time by remaining at an administrated portion as well as a pharmaceutical composition produced by the same. Specifically, the present invention relates to a process for producing a pharmaceutical composition, comprising steps of: mixing and heating a first phase, prepared by mixing a polyhydric alcohol and a salt, and a second phase containing a water-soluble polymer under a reduced pressure, before evaporating substantially all water in the first phase by mixing and heating a mixture of first and second phases under a reduced pressure or after evaporating substantially all water in the first phase by mixing and heating the first phase under a reduced pressure; and adding a third phase containing an active ingredient unstable against water and mixing them to obtain the pharmaceutical composition, as well as a pharmaceutical composition produced the same.