The alkoxyallenes (1-5) are polymerized by BF(3)OEt(2) (2 mol %) or CH3SO3H (2 mol %) in dichloromethane at -50 degrees C. The cationic polymerizability of alkoxyallenes decreased in the following order : i-Pr > i-Bu > Pr > Et > Me. These results might be explained due to the electron-donating ability of the alkyl groups. The structures of all obtained polymers were formed by polymerizing only the 1,2-double bond of alkoxyallenes. The polymerization by BF(3)OEt(2) decreased the content of the double bonds in the obtained polymer to 21-29 mol % of the theoretical content, whereas the polymerization by CH3SO3H suppressed the decrease of the double bond content in the obtained polymer.