An amphiphilic molecule bearing a coumarin moiety attached to a water-soluble fullerene via an alkyl linker forms a water-soluble fullerene bilayer vesicle in water that spontaneously agglomerates and fuses upon standing. The agglomeration-fusion ability of the vesicle was endowed probably by the intervesicular interaction between the coumarin group and the fullerene core, as judged by the lack of such ability for the vesicles bearing only alkyl groups and by complete inhibition by conversion of the coumarin group into a photodimer.