To investigate the influence of support porosity parameters e.g., average pore volume (APV), pore diameter (PD), and pore surface area distribution (PSAD) on activity-profile of catalyst and comonomer incorporation, a series of silica-supports with different porosity were prepared through solgel method and used to synthesize corresponding (SiO2/MgCl2/TEOS/TiCl4) catalysts. Polymerization of ethylene/butene-1 showed that increasing of APV from 0.75 to 2.2 cm3 g?SiO2-1 increase initial activity from 120 to 400 (gpoly/gcat.bar.hr) followed by appearance of secondary peaks in activity-profile which could be attributed to the variation of PSAD. It is found that the effect of support in polymerization is a complicated issue which depends not only on the porosity parameters also on the comonomer concentration. The catalyst with PD of 300 angstrom gives higher comonomer incorporation and polymers with 1520% lower crystallinity in contrast to catalyst with PD of 100 angstrom. Porosity effect was quantitatively studied by modifying of conventional Z-N catalyst polymerization mechanism through introducing fragmentation term to achieve a new tool in designing and developing of polyolefin catalysts. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011