Morphological transition of two types of multiblock terpolymers with composition has been investigated. One is undecablock terpolymers of the PISISISISIP type, while the other is hexablock terpolymers of the PISISI type, where P, I, and S denote poly(2-vinylpyridine), polyisoprene, and polystyrene, respectively. These polymer samples were prepared on the basis of anionic polymerization method. The volume fractions of P, phi(P), of the former are 0.08, 0.21, 0.53, whereas those of the latter are 0.64, 0.75, and 0.87. Nanophase-separated structures were observed by TEM and SAXS, and it was confirmed that their hierarchical morphology transforms from spheres-in-lamellae structure into cylinders-in-lamellae, lamellae-in-lamella, and coaxial cylinderical structures and finally into onionlike spherical structure with increasing volume fraction of the P component. From these results, it has been found that morphological transition of multiblock terpolymers takes place obeying conventional rule, i.e., the domain shape of P component varies as sphere-cylinder-lamella-matrix as phi(P) increases with keeping hierarchical lamellar structure from I and S.