A rapidly cooled poly(dioctylsilane) (PDOS) is found to exhibit unprecedented thermochromic behavior showing lambda(max) at 353 nm as the major absorption which is accompanied with a minor one at 375 nm. On heating, the absorption at 353 nm begins to decrease at 250 K and, then, the minor one does at 280 K. Similar temperature dependent behavior is observed in the X-ray powder diffraction around 2 theta = 6 degrees which is ascribable to inter-chain alignment. On heating diffraction at 2 theta = 6.2 degrees (d = 1.43 nm) disappears firstly, and then that at 6.4 degrees (d = 1. 38 nm) is displaced by the diffraction at 5.8 degrees (d = 1.52 nm).