The monomer, 1,2-diethynylbenzene. was prepared by the reaction of 1,2-bis (trimethylsilylethynyl) benzene with KF, and homopolymerization and copolymerization with diethyldipropargyl malonate were carried out by various metathesis catalyst systems such as WCl_6- and MoCl_5- based catalysts associated with organo-aluminum and tin compounds. It was generally observed that the MoCl_5- based catalysts were more effective for both the homopolymerization and copolymerization, and polymer yields increased with increasing initial concentration of the monomer and mole ratios of the catalyst to the monomer. The resulting dark red homopolymer, poly(1,2-diethynylbenzene), is hardly soluble in common organic solvents such as chloroform and tetrahydrofuran, whereas the violet copolymers which have number average molecular weight of ca. 3×10⁴ are soluble in those solvents. The structure of the copolymers was identified by NMR and IR spectroscopies. From the spectral and solubility data, it is proposed that the copolymer structure is a cyclized form with conjugation. Homopolymer and copolymer(1 :1) are thermally stable up to 230℃ and 320℃, respectively and conductivities of the I₂-doped polymers at room temperature were found to be about 10^-6S/cm.