A new monocyclopentadienylamido complex, [eta (5):eta (1)-(2,3-Me(2)Benz[e]Ind)(SiMe2NBu)-Bu-i]TiCl2 (I), was synthesized as catalyst precursor. The studies on the homopolymerization and copolymerization of 4-methyl-1-pentene (P) and ethylene (E) were presented, by comparing complex I with other CpA complexes and Cp2M zirconocenes. The complex I, activated with methylaluminoxane, provided an enhanced copolymerization activity, an excellent incorporation of 4-methyl-1-pentene into the polyethylene chain, and an increased copolymer molecular weight. Analysis of C-13 NMR spectra of polymers, combined with the monomer reactivity ratios and the polymerization results, demonstrated that the regioselectivity of monomer insertion, tacticity, productivity, molecular weights, and polymer microstructure are significantly dependent on the ligand substitution pattern and the metal atom in CpA complexes. The CpA I-derived poly(4-methyl-1-pentene-co-ethylene)s contained a significant amount of regioirregular arrangement of 4-methyl-1-pentene unit, but with no virtually consecutive 8-methyl-1-pentene sequence. In contrast, the [eta (5):eta (1)-(Me4C5)(SiMe2NBu)-Bu-t]TiCl2 (IV)-derived copolymers revealed the small clustered sequence (e.g., EPPE) but without any regioirregular arrangement of 4-methyl-1-pentene units. The copolymers prepared with [eta (5):eta (1)-(Flu)(SiMe2NBu)-Bu-t]TiCl2 (VI) not only showed quite different microstructure from that based on catalysts I and IV but also manifested the more pronounced tendency to form an alternating distribution of monomers in the polymer chains. Furthermore, the VI-derived copolymer contained neither a regioregular insertion of comonomer nor the consecutive 4-methyl-1-pentene sequences.