N,N-Dimethylanilinium salt of molybdenum disulfide (MoS2) was developed as a novel cocatalyst for metallocene catalysts. The cocatalyst is composed of N,N-dimethylanilinium ion as a cationic part and "topotactic" reduction product of MoS2, obtained by acquisition of an electron by neutral host lattice Of MoS2 without structural alteration, as an anionic part. In ethylene polymerization, addition of the N,N-dimethylanilinium salt Of MoS2 to the bis(indenyl)zirconium dichloride (Ind(2)ZrCl(2))/triethylaluminum (Et3Al) catalyst improved the catalytic activity per mmol of Ind(2)ZrCl(2). The catalytic activity of this system activated by addition of the cocatalyst depended significantly on the amount of the cocatalyst and the N,N-dimethylanilinium ion content in the cocatalyst. Poly(ethylene) and poly(ethylene-co-1-hexene) obtained with the metallocene catalyst activated by addition of the cocatalyst have typical features such as narrow molecular weight distribution and narrow composition distribution like polymers obtained with conventional metallocene catalysts. (C) 2003 Elsevier Science B.V. All rights reserved.