A solid pharmaceutical preparation of solifenacin or a salt thereof, the preparation being stable and inhibited from decomposing with time when supplied to clinical fields. In a pharmaceutical preparation containing solifenacin or a salt thereof, the compound in an amorphous form was revealed to be causative of cardinal-drug decomposition with time. The composition for a solid pharmaceutical preparation of solifenacin or a salt thereof contains solifenacin or its salt each in a crystalline form, and the content of the compound in an amorphous form in the composition is within the range which exerts no influence on product stability. Also provided are: a process for producing the composition; and a medicinal composition for solid pharmaceutical preparations which contains solifenacin and an amorphization inhibitor. |