1,4-Bis(4-alkylpyridinium)butadiyne triflate (2a and 2b) that was prepared by the reaction of 1,4-bis(4-pyridyl)butadiyne (1) with alkyl trifluoro-methanesulfonate, was found to grow into a large crystal as a result of the quaternized structure. The thermal treatment of 2a and 2b gave rise to 1,4-addition polymerization to yield the polydiacetylene. The third-order nonlinear optical susceptibility [chi ((3))] of the polymer was determined by the femto-second Z-scan method to exhibit the remarkable high value of 1.1 X 10(-11) esu at 650 mn.