Copolymerization of propene and small amount of ethylene was conducted with the TiCl4/DBP/MgCl2-Al(i-C4H9)(3) catalyst in the presence and absence of 1-allyl-3,4-dimethoxybenzene(ADMB). Addition of ADMB caused a decrease in the ethylene content in copolymer with an increase in the activity. From a detailed analysis of the copolymers fractionated with boiling diethylether, it was found that the ADMB-containing system gives ether-soluble polymers with higher molecular weight and narrower molecular weight distribution as well as less content of regioirregular sequences of propene. The microstructures of the ether-soluble parts suggested that ADMB might accelerate the propene polymerization at the aspecific sites formed.