SUMMARY: Propylene polymerization was conducted with Ph 2 C(R-Cp)(Flu)ZrCl 2 [R = Me, i-Pr, PhCH 2 , Me 3 Si] catalysts in combination with methylaluminoxane (MAO) and dimethylanilinium tetrakis(pentafluorophenyl)borate (Me 2 PhNH N B(C 6 F 5 ) 4 ) as cocatalyst; the dependence of the stereoregularity of poly(propylene) on cocatalysts and bulkiness of the substituents in b -position of the cyclopentadienyl ligand was studied. Methyl and i-propyl substituted metallocene catalysts produce hemi-isotactic poly(propylene). These results are in good agreement with the results of the isopropylidene bridged metallocene analogue. The benzyl substituted metallocene catalyst produces syndiotactic poly(propylene) regardless of the cocatalyst. This means that this substituent group does not affect migration insertion of propylene. Stereoregularity of poly(propylene) obtained with diphenylmethylidene(3-trimethylsilylcyclopentadienyl)(fluorenyl)zirconium dichloride (Ph 2 C(Me 3 SiCp)(Flu)ZrCl 2 ) as a catalyst was significantly influenced by the cocatalyst. Me 2 PhNH N B(C 6 F 5 ) 4 /triisobutylaluminium(i-Bu 3 Al) produces poly(propylene) with 65% racemic and 23% meso pentads at 40 8 C, whereas the MAO activated catalyst produces isotactic rich poly(propylene). Fractionation experiments indicated that Me 2 PhNH N B(C 6 F 5 ) 4 /i-Bu 3 Al forms two active sites, one of them being the same as that of the MAO activated catalyst, the other one producing syndiotactic rich poly(propylene).