The solid-state polymerization of a diacetylene, 1,11,13,23-tetracosatetrayne, was studied using x-ray powder diffraction and electron diffraction. it is shown that the material exhibits polymorphism. Thermochromic transitions, which are generally observed for diacetylenes, are related to the particular crystalline phase using x-ray powder diffraction. The unit cell dimensions and space group of one polymorph were determined by electron diffraction analysis : a = 20.83 Angstrom A, b = 4.84 Angstrom A, c = 10.08 Angstrom A, beta = 92.4 degrees, space group : P2(1)/n.