AbstractCopolymerization of propene with 1‐hexene was performed at 40°C under atmospheric pressure using both aspecific and isospecific catalysts composed of TiCl3/MgCl2and Al(C2H5)3, and of Solvay type TiCl3and Cp2Ti(CH3)2(Cp: cyclopentadienyl), respectively. The isospecific catalyst gave two kinds of copolymers with different content of 1‐hexene, whereas the aspecific catalyst gave a uniform copolymer abundant in 1‐hexene. Both copolymers produced with the isospecific catalyst were found to show isotactic stereoregulation in the propylene units. From these results, it was concluded that the catalyst composed of Solvay type TiCl3and Cp2Ti(CH3)2has two kinds of isospecifically active species which differ in the monomer reactivity ratio for propene‐1‐hexene copoly