A series of 1-(2-benzhydrylnaphthylimino)-2-phenyliminoacenaphthylene derivatives (L1–L5) was synthesized, characterized, and then reacted with (DME)NiBr₂ to form the corresponding [1-(2-benzhydrylnaphthylimino)-2-phenyliminoacenaphthyl]nickel bromides (C1–C5). All nickel complexes were fully characterized by their FT-IR spectra and elemental analysis. The molecular structures of the representative complexes C1 and C4 were also determined by single-crystal X-ray diffraction. On activation with either methylaluminoxane (MAO) or diethylaluminum chloride (Et₂AlCl), all title nickel complexes showed high activities toward ethylene polymerization; the resulting polyethylenes showed molecular weights higher than those obtained by using the nickel analogues bearing (2-benzhydrylnaphthylimino)pyridines and also had branches lower than those obtained by using other diiminoacenaphthylnickel analogues. Therefore, the modification of ligands could affect the catalytic behavior of their nickel complexes in order to tailor the molecular weights and branches of the resulting polyethylenes.