The wave dispersion of cubic susceptibility chi((3)) of green-form polydiacetylene, which can be obtained by annealing a diacetylene Langmuir-Blodgett film before photo-polymerization, was measured for the first time and compared with that of a blue form obtained from the same monomer without the anneal. The maximum chi((3)) of the green form (0.97 x 10(-10) esu) is smaller than that of the blue form (1.2 x 10(-10) esu). This result indicates that though the green form has a highly ordered structure by the anneal, pi-electron delocalizability along its polymer main chain decreases.