A solid pharmaceutical preparation of solifenacin or asalt thereof, the preparation being stable and inhibited fromdecomposing with time when supplied to clinical fields. Ina pharmaceutical preparation containing solifenacin or a saltthereof, the compound in an amorphous form was revealed to becausative of cardinal-drug decomposition with time. Thecomposition for a solid pharmaceutical preparation ofsolifenacin or a salt thereof contains solifenacin or its salteach in a crystalline from, and the content provided are: aprocess for producing the composition； and a medicinalcomposition for solid pharmaceutical preparations whichcontains solifenacin and an amorphization inhibitor.
