The present invention relates to a method for the prepolymerization of -olefin
in the presence of a catalyst system which comprises (a) a magnesium supported
solid complex titanium catalyst and (b) an organometallic compound of metal of
Group I or III of the Periodic Table, characterized in that an inert solvent having
high viscosity with molecular weight of 300 g/mole or more is used as a reaction medium.
