A method for producing high reactive polybutene (HRPB), in which carbon-carbon double bond is positioned at an end of polybutene, is disclosed. The high reactive polybutene having 300.about.5000 of number average molecular weight (Mn) can be produced from a raw material containing isobutene, wherein a polymerization reaction of the isobutene is carried out in the presence of a catalyst system including secondary alkylether, tertiary alcohol, and boron trifluoride, the amount of boron trifluoride is 0.05.about.1.0 weight part per 100 weight part of isobutene, the mole ratio of a co-catalyst including secondary alkylether and tertiary alcohol:boron trifluoride is 1.0.about.2.0:1, and the mole ratio of secondary alkylether:tertiary alcohol is 0.5.about.1.2:1.