To provide a method for performing the slurry or solution polymerization of an α-olefin without forming polymer scales on the surface of a polymerizer or its agitator.

A slurry or solution of at least one α-olefin and at least one diolefin as an optional component is mixed with at least about 0.3wt.%, based on the total weight of the polymer to be formed, inert particulate substance having a mean particle diameter of about 0.1 to about 10μm, and the obtained mixture is brought into contact with a catalyst system adapted so that it may catalyze the polymerization of the α-olefin and at least one diolefin as an optional component in the mixture.