To investigate the effects of branching position on morphology of graft copolymers, a series of styrene-g-isoprene graft copolymers with the same backbone chain length and also with the same graft chain length but with different graft junction points was prepared by anionic polymerization applying a new preparation method in three steps; (1) coupling of living polystyrene onto telechelic polystyrene, (2) introduction of reactive but non-polymerizable vinyl groups onto the two connecting points of triblock polystyrene, (3) grafting of living polyisoprene onto polystyrene backbone with two reactive sites obtained in step (2). The samples were confirmed to have well-defined molecular structure as designed by characterization using osmometry, GPC, and 1H NMR. Seven graft copolymers were prepared, which have almost the same total chain length, their constant polyisoprene volume fraction, φPI, being around 0.5. From morphological studies, the graft copolymers form cylindrical structures, not alternating lamellar structures, even though the volume fraction of graft chains is about 0.5. It turned out that domain spacing has minimum for a molecule whose two junction points divide backbone chain into three chains with the same chain length.