(4-Vinylbenzyl)polystyrene macromonomer (PStM, M-n = 5.4(5) x 10(3), M-w/M-n = 1.0(3)) was living-anionically polymerized by sec-BuLi to produce the (PSt)(n)(-) star polymer under high vacuum at room temperature. Then, isoprene (Is) was sequentially copolymerized by (PSt)(n)(-) to yield the (PSt)(6.1)-s-(PIs)(1) star block copolymer (M-n = 6.3(9) x 10(4), M-w/M-n = 1.0(4)) having a narrow PIs composition distribution. Similarly, the (PIs)(6.6)-s-(PSt)(1) star block copolymer (M-n = 10.(8) x 10(4), M-w/M-n = 1.0(4)) was prepared using (4-vinylbenzyl)polyisoprene macromonomer (PIsM, M-n = 5.1(9) x 10(3), M-w/M-n = 1.0(4)). The synthetic route by which the PIs(-) carbanions copolymerize PStM was found to be unsuitable for preparing (PIs)(1)-star-(PSt)(n). The resultant star polymers and star block copolymers were characterized by a special analysis using a gel permeation chromatograph equipped with a low-angle laser light-scattering detector. The living mechanism of the macromonomers polymerization was discussed from the viewpoint of initiation efficiency. The asymmetric architecture of the resultant samples was also discussed on the basis of the relationship between molecular weights and molecular dimensions using a model of regular comb-shaped polymers. Two films of the (A)(n)-star-(B)(1) star block copolymers showed a clear microphase-separated structure as observed by transmission electron microscopy. Their morphologies shifted to the higher star polymer content side of the morphological transition line for linear block copolymers. This interesting gap in the morphology between the star block copolymers and linear block copolymers was quantitatively explained by a volume fraction and an asymmetric factor.