The invention concerns fumarate salts of solifenacin, as well as pharmaceutical compositions comprising fumarate salts of solifenacin. The invention furthermore concerns a process for preparing solifenacin and salts thereof. The fumarate salt provides improved properties over the known solifenacin salts, especially in terms of its stability. The novel process for its preparation is furthermore improved over known processes for preparing solifenacin in that it provides a higher yield and recovers a greater amount of starting material.