A novel substituted diacetylene, 2-methyl-4-(6"-octadecoxy-2",4"-hexdiyne)oxy-4’-nitroazobenzene (4) was synthesized. Its structure was confirmed by elemental analysis, IR spectroscopy and mass spectrometry. A stable Langmuir film of 4 was formed at the air-water interface and its Langmuir-Blodgett (LB) film was fabricated and characterized. Solid state polymerization of the LB films was performed by Co-60 radiation at room temperature.