The polymerization of ethylene with rac-Et(1-indenyl)(2)ZrCl2/MAO catalyst supported on ultraporous and spherical pseudo-inverse opal silica (PIOS) particles with unique morphology is reported. The novel silica particles with an inverse opal-like structure provide wide-open pore and surface structures favorable for the catalyst deposition and monomer access with minimal intraparticle diffusion resistance. The metallocene catalyst supported on the PIOS support exhibited very high initial catalyst activity and longer catalyst lifetime compared with conventional silica-supported catalysts. The experimental data that show the effects of support geometry on the catalytic activity, catalyst particle fragmentation, polymer particle morphology, and polymer molecular weight distribution in ethylene polymerization are presented.