The copolymerization of propylene with 1-octene was carried out with rac-dimethylsilylbis(2,4,6-trimethylindenyl) zirconium dichloride as a catalyst activated by methylaluminoxane (MAO) and an MAO/triisobutylaluminum mixture. The copolymerization conditions, including the polymerization temperature, Al/Zr molar ratio, and 1-octene concentration in the feed, significantly influenced the catalyst activity, 1-octene incorporation, polymer molecular weight, and melting temperature. The addition of 1-octene to the polymerization system caused a decrease in the activity, whereas the melting temperature and intrinsic viscosity of the polymer increased. The microstructure of the propylene-1-octene copolymer was characterized by C-13 NMR, and the reactivity ratios of the copolymerization were estimated from the dyad distribution of the monomer sequences. The amount of regioirregular structures arising from 2,1- and 1,3-misinserted propylene decreased as the l-octene content increased. The influence of the propagation chain on the polymerization mechanism is proposed to be the main reason for the changes in the reactivity ratios and regioirregularity with the polymerization conditions.