Provided is a pharmaceutical composition which enables the inhibition of formation and/or enlargement of cerebral aneurysm or the regression of cerebral aneurysm. The pharmaceutical composition for the inhibition of formation and/or enlargement of cerebral aneurysm or for the regression of cerebral aneurysm of the present invention, which includes a S1P1 receptor agonist as an active ingredient, enables the inhibition of formation and/or enlargement of cerebral aneurysm or the regression of cerebral aneurysm, and enables the prevention and/or treatment of a disease associated with cerebral aneurysm.