Catalyst particle size is an important parameter in the polymer industry. A series of supports with different textural properties (silicas prepared by different routes), surface sites (alumino-silicate, silica-zirconia, magnesia-silica supports, and methylaluminoxane-modified silica) and crystallinity (amorphous, lamellar, and crystalline materials) were investigated in the sequential grafting reaction of two metallocene catalysts, Cp2ZrCl2 and (n-BuCp)(2)ZrCl2, in a 1:3 ratio. The catalyst systems were analyzed by Rutherford backscattering spectrometry, atomic force microscopy, small angle X-ray scattering, extended X-ray absorption fine structure spectroscopy, and nitrogen adsorption. All of the systems were shown to actively polymerize ethylene when methylaluminoxane was used as the cocatalyst. Experimental results are discussed in terms of the relationships between the radius of gyration of secondary particles and catalyst activity. A radius of gyration in the range of 8-9 nm was shown to be associated with higher catalyst activity.