Substituted polyacetylenes have been extensively studied as a representative class of organic semiconducting polymers. The functional substituents in polyacetylene can add the peculiar properties to conjugated polymer system. Here, we prepared poly(3-ethynylthiophene) by the polymerization of 3-ethynylthiophene by various transition metal catalysts in a moderate yield. The resulting polymer was completely soluble in such organic solvents as chloroform, THF, toluene, chlorobenzene, etc. The electro-optical properties of poly (3-ethynylthiophene) were measured and discussed. The cyclic voltammograms of poly(3-ethynylthiophene) exhibited reversible electrochemical behaviors between the doped and undoped peaks.