Propene, 1-butene and 1-hexene polymerization was conducted with a mixture of rac- and meso-[dimethylsilylenebis((2,3,5-tetramethyl-cyclopentadienyl)] zirconium dichloride (Me2Si(2,3,5-Me3Cp)(2)ZrCl2) (1) combined with methylaluminoxane triethylaluminium (AlEt3)/triphenylcarbenium tetrakis(pentafluorophenyl)borate (Ph3CB(C6F5)(4)) (2) and triisobutylaluminium (AliBu(3))/Ph3CB(C6F5)(4), respectively, as co-catalyst systems. The ratios of polymerization rates R-p(rac)/R-p(meso) were changed with the combined cocatalysts. It was found that in the case of using trialkylaluminium/2 as co-catalyst R-p(rac)/R-p(meso) is lower than when using MAO in any kind of alpha-olefin polymerization.