Poly (β-ethynylnaphthalene), which has not been previously prepared and characterized in detail, was prepared with a Ziegler-Natta type catalyst. The polymer is reddish in color, soluble in aromatic solvents, and gives a positive color test for conjugation with antimony trichloride. The polymer has a molecular weight of up to 2091. Its IR and W spectroscopic characteristics are in accord with a modified conjugated polyene structure. It is thermally stable up to 470°, and probably partially crystalline.