PURPOSE: To prepare a rubbery ethylene compolymer having excellent randomness with a high yield, by using a catalytic system consisting of a titanium tetrahalide, a specified tetravalent titanium compd., an org. aluminum compd. and an org. hydroxyl compd.

CONSTITUTION: A catalytic system is prepared from a titanium tetrahalide (A) (e.g., titanium tetrachloride), a tetravalent titanium compd. (B) of the formula (wherein R is a 1W20C hydrocarbon group; X is halogen; n is 0W3) [(e.g., Ti(OC2 H5)Cl3 or Ti(OC3H7)Cl3)], an org. aluminum compd. (C)(e.g., triethylaluminum) and 0.1W0.095 mole of an org. hadroxyl compd. (D) in terms of functional group based on 1mol of the component C (e.g., n-butyl alcohol). An ethylene compolymer is obtd. by copolymerizing ethylene with a copolymerizable monomer (e.g., propylene) in the presence of this catalytic system.