Propylene polymerization was performed using three constrained geometry catalysts: 2-(tetramethylcyclopentadienyl)-4,6-di-tert-butylphenoxytitanium dichloride (1), 2-(tetramethylcyclopentadienyl)-6-tert-butylphenoxytitanium dichloride (2), and 2-(tetramethylcyclopentadienyl)-6-phenylphenoxytitanium dichloride (3) with Al( i Bu) 3 /[Ph 3 C] + [B(PhF 5 )] 4 − as co-catalyst. The substituent effect of the ligand and the effect of the Al/Ti molar ratio on the catalytic properties were investigated. The catalytic activity decreases in the order of 1>2>3. The 13 C NMR results show that the polymers are basically atactic polypropylene with some 2,1-insertion and 1,3-enchainment units in the polymer chain, and the end groups are mainly vinylidene (CH 2 CMe–) and vinyl (CH 2 CH–) together with a small amount of propenyl (CH 3 CHCH–). A possible chain propagation and termination mechanism of the propylene polymerization was discussed.