Three polystyrene-block-polyisoprene-block-polystyrenes (SIS) with different compositions were prepared and cyclized by the coupling reaction between two end groups on the same molecules. Ring-shaped polystyrene-block-polyisoprenes (SI) were isolated from the coupling products by GPC fractionation. They were ozonized in order to decompose the polyisoprene blocks selectively referring to the linear molecule. GPC analysis of the decomposed products obtained by ozonolysis quantitatively confirmed that the fractionated products include ca. 90% ring molecules. The morphological transition of the ring-shaped block copolymers depends on composition in essentially the same manner as that of the linear triblock copolymers, whereas the domain spacings of SI ring-shaped block copolymers were all smaller than those of the corresponding SIS linear triblock copolymers, which is attributed to looped chain conformation.