A living block copolymerization of allene derivatives with 1-phenylethyl isocyanide (3) using [(allyl)NiOCOCF3](2) (1) is described. After complete polymerization of allene monomers such as n-octyloxyallene (2A) with 1, further addition of 3 to the reaction system yielded the corresponding block copolymers in high yield. For instance, a block copolymer (4A, M(n) = 39,600, M(w)/M(n) = 1.20) was obtained in 96% yield by the addition of 3 ([3]/[1] = 250) to the living solution of poly(n-octyloxyallene) (M(n) = 14,400, M(w)/M(n) = 1.03) prepared by the polymerization of 2A in the ratio of [2A]/[1] = 90. The resulting copolymer was a brownish orange gum or a solid, depending on the length of each of the segments. The solubility of the block copolymers could be controlled by the allene components. The copolymer of 2A with 3 having appropriate length of segments was soluble in n-hexane, while that of methoxyethoxyethoxyallene (2D) with 3 was soluble in methanol.