Ethene/propene copolymerizations were performed with a catalytic system composed of a metallocene and an alumoxane. The role played by the alumoxane was investigated by comparing the effects of three different compounds: poly(methylalumoxane) (MAO), tetraisobutylalumoxane (TIBAO), and tetraisooctylalumoxane (TIOAO). A thorough comparison was performed using rac-ethylenebis(tetrahydroindenyl)zirconium dichloride (r-EBTHIZrCl2) as the metallocene. Further data were obtained with isopropylidenebis(3-tert-butyl-cyclopentadienyl)zirconium dichloride (r-Me2C(3-t-BuCp)(2)ZrCl2) and dimethylsilylenebisfluorenylzirconium dichloride (Me(2)SiFlu(2)ZrCl(2)). Main parameters of copolymerization and copolymers were determined. MAO gives rise to higher polymerization activities and lower molecular masses of the copolymers. A higher productivity is obtained with TIOAO than with TIBAO, whereas these two alumoxanes behave very similarly in determining the copolymer properties. A statistical elaboration allowed to derive the reactivity ratios of the comonomers. The copolymer microstructure is essentially due to the metallocene, even though a MAO-based catalytic system shows a slightly higher reactivity for propene.