Polyethylene (PE) particles are produced by a catalyst prepared by contacting a (C4H9Cp)(2)-ZrCl2/MAO pre-mixing solution with SiO2 support. These particles have a large granular size and very few fine particles compared with those derived from a catalyst prepared by adsorption of (C4H9Cp)(2)ZrCl2 onto methylaluminoxane modified SiO2. The amount of Al in the pre-mixing catalyst has an important effect on its activity and the PE particle size distribution. The optimal concentration is about 30 wt.-%. The PE particles produced using a pre-mixing catalyst consist of globules with randomly oriented fiber structure on the surface, whereas those produced using adsorption catalysts have worm-like fibrils protruding from the PE globule surface.