The polymerization of indene was investigated in the presence of group V and Ⅵ transition metal halides such as WCl₆, MoCl₅, TaCl₅, and NbCl₅ as catalysts under various reaction conditions. Indene was found to be easily polymerized with a high initial rate by these transition metal catalysts. Almost quantitative conversion and somewhat high molecular weight of polymer were obtained in chlorobenzene when the monomer to WCl₆ mole ratio 200. It was observed that the results of polymerization depended strongly on the monomer to catalyst mole ratio, and aromatic solvents generally gave better results in conversion and molecular weight of the polymers than aliphatic ones. The copolymerization of indents with acenaphthylene by WCl₆ in chlorobenzene also proceeded quantitatively The structures of the resulting homo and copolymers were characterized by means of several spectroscopic analyses.