Abstract Soluble TiCl3 complex catalysts were prepared by reduction of TiCl4 with hydrogen in the presence of Pd-carbon and ether in a halogenated hydrocarbon solvent. When copolymerization of ethylene with propylene was carried out with the soluble TiCl3 catalysts, the catalytic activities were very high, and copolymers obtained showed low crystallinity. When a small amount of a metal chloride was added to the soluble TiCl3 catalysts, it was found that the catalytic activity increased and the crystallinity of copolymers obtained was lower compared with those of the copolymers prepared by the original soluble TiCl3 catalysts. The copolymers obtained by the soluble TiCl3 catalysts showed high tensile strength (TB) and elongation at break (EB). From these results, it is concluded that the large values of TB and EB are caused from the microblock sequences of ethylene.