The block copolymerization of alkoxyallenes (2a; n-octyloxyallene and 2b; n-butoxyallene) with phenylallene (3) was carried out by [(pi-allyl)NiOCOCF3](2) (1) in toluene by the sequential addition of the two monomers. In spite of rather different polymerizability between 2 and 3 (i.e., 2 has ca. 70 times larger kinetic coefficient than 3), block copolymers having narrow molecular weight distributions were obtained successfully by controlling the reactivity of the propagating end with the additives such as triphenylphosphine (PPh3) and copper(I) iodide. In the case of the copolymerization of 3 with 2, the addition of PPh3 was effective for the control of the polymerization step of 2. The block copolymers with controlled segment length and narrow molecular weight distributions (M-W/M-n < 1.08) were obtained almost quantitatively. Conversely, when the copolymerization was started from 2, the control of the first stage required PPh3 as a ligand of the initiator which interrupt the second polymerization of 3. However, block copolymers with narrow molecular weight distributions (M-W/M-n < 1.03) were obtained simply by adding copper (I) iodide in the polymerization stage of 3.